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Documentation:FIB book/The Effectiveness of Scrum Caps in Preventing Head Injury in Rugby

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1.0 Rugby and Head Collisions

Figure 1. 2022 rugby union test match between Italy and South Africa at Stadio Luigi Ferraris, Genoa, Italy 19th November 2022
Figure 2. Image showing Cauliflower Ear.
Figure 3. 2014 Women's Championship Image depicting a Rugby Scrum.

Rugby is widely recognized as one of the most dangerous field sports, characterized by frequent high-impact collisions and minimal protective equipment. Unlike American football, where players are required to wear hard-shell helmets and pads, rugby players have limited protection and may only opt to wear a soft-shell head covering called a scrum cap (Figure 1). These caps were originally introduced to prevent cauliflower ear (Figure 2), a deformity caused by repetitive trauma to the ear tissue [1]. The term “scrum” refers to a specific formation in rugby where players interlock and push against one another (Figure 3) —placing ears and faces in close contact with opponents’ bodies and increasing the risk of cuts, abrasions, and ear injuries [2].

While such soft-tissue injuries are common, the most frequent and severe injuries in rugby involve the head and neck, with the neck being among the most commonly injured body parts[3]. Epidemiological data highlight the magnitude of the issue: during the 2019 Rugby World Cup, there were approximately 68 head injuries per 1,000 player-hours, with 23 of these diagnosed as concussions[4]. This corresponds to an estimated 6.8% probability of sustaining a head injury for every hour played, emphasizing the significant risk rugby players face.

Despite the high incidence of concussions, the introduction of rigid headgear—such as that used in American football—has been resisted for two main reasons. First, rigid protective gear can increase the risk of injury to other players, as collisions with hard surfaces can cause additional harm[5]. This rationale also explains why rugby players do not wear shin guards or rigid groin protection. Second, the “risk compensation” effect suggests that players wearing extensive protective gear may behave more aggressively, falsely relying on equipment to keep them safe[3]. For these reasons, World Rugby regulations continue to prohibit hard-shell helmets and limit approved headgear to soft-padded scrum caps.

Importantly, scrum caps are not designed to prevent concussions or skull fractures. World Rugby explicitly states that their intended purpose is to protect against superficial head and ear injuries, not brain trauma[6]. However, the padded appearance of scrum caps has led many players and parents to perceive them as a form of concussion protection, and some manufacturers market them using language that implies impact absorption or “knock reduction”[7]. This discrepancy between perceived protection and actual function raises critical safety and ethical concerns.

Given the prevalence of head injuries in rugby and the misconceptions surrounding protective gear, it is essential to evaluate whether scrum caps offer any measurable protection beyond reducing abrasions. This literature review will examine empirical studies assessing scrum cap performance—such as drop tests, head acceleration measurements, and impact attenuation studies—to determine whether these caps provide a meaningful reduction in head injury risk. Understanding their true protective capacity has important implications for injury prevention, player safety policy, and the long-term neurological health of rugby athletes, who may otherwise face chronic conditions such as post-concussion syndrome, cognitive impairment, and even early-onset neurodegenerative diseases.

2.0 Previous Work and Current Innovation

Early Studies of Rugby Head Impacts and Scrum Caps

A 2000 study used video analysis to investigate head kinematics in Rugby Union, Rugby League, and Australian Rules Football, where hard-shell helmets are also not permitted. They found that out of 100 incidents of concussion, 86% of impacts occurred in the anterior half of the head, while 10% of concussions occurred from impacts to the occipital region[8].

When comparing scrum caps made of multiple connected foam cells to those made of continuous pieces of foam, it was found, in Knouse et al., that continuous foam caps could potentially provide better distribution of forces upon impact[9]. This study also found that the efficacy of scrum caps also differed significantly depending on the location of impact, with impacts to the occipital region experiencing the most severe impacts. They suggested that the posterior lace-up design of the helmet was contributing to this, noting that the standards at the time did not require padding in the occipital region, and mandated that padding in the occipital region not exceed 0.5cm, while all other regions required a 1cm padding thickness.[9]

Early studies also found that scrum caps tended to be less effective with repeated impacts, suggesting that the foam used in the caps was not able to fully regain its original shape or thickness. With players typically experiencing multiple impacts during a single game, this rapid decline suggests that scrum caps may not be suitable for protecting players from injury.[9]

Recent Studies of Rugby Head Impacts for Headgear Testing

While World Rugby has a standard method for testing scrum caps, most researchers perform their own variation of it in their own testing.[6][10] This review explores rugby headgear drop test kinematics across four different variations of the standardized World Rugby test. These four variations involve using the same methods as defined by World Rugby, but with three different impact surfaces, both with and without the ATD neck included. These tests will be referred to as Test 1 through 4. We have chosen to include images of experimental set-ups from the aforementioned study by Stitt et al., 2022 to better demonstrate these subtle differences that cause each method to yield different results.

Test 1: Headform Only with Flat Steel Impact Surface

Figure 4. Headform-only test with flat steel impact surface.[10]

Test 1 used a headform only with a flat steel impact surface (Figure 4, Row 1).[10] This test produced the highest impact force and largest acceleration values of each test. The impact was short in duration, resulting in there being little secondary motion or significant secondary impact due to the headform having a low rebound height from the flat steel impact surface.

Test 2: Headform and Neck with MEP Pad Impact Surface

Test 2 used a headform with a neck onto a flat modular elastomer programmer (MEP) pad impact surface (Figure 4, Row 3). MEP pads are often used for helmet testing since they are a consistent impact material, and due to MEP values being specified in many helmet and headgear testing standards.[11] The initial impact lasted for a shorter time than models without necks, but the neck itself did not significantly change peak acceleration values. This test is relatively more realistic due to the flexible Hybrid III ATD neck that allowed for head rotation. As a result, secondary impacts were introduced when the model rebounded.[10]

Test 3: Headform Only with MEP Pad Impact Surface

Test 3 was the same set-up as Test 2, but without a neck (Figure 4, Row 2).[10] This method had the higher rotational acceleration peaks than Test 2, but lower overall accelerations than Test 1. The main takeaway from this technique was highlighting how rotational stiffness increased along with sudden changes in motion without a neck present. These results were largely due to the rigid occipital joint movement.

Test 4: Headform and Neck with Angled MEP Pad Impact Surface

Test 4 had the same set-up as Test 2, but on an angled MEP surface instead of flat (Figure 4, Row 4).[10] This method had the highest ratio of rotational to linear motion, but the lowest peak linear and rotational accelerations. Taking these results into account in combination with the angled surface, Stitt et al., 2022 found that this test was the most representative of real-world oblique impacts and best simulated realistic head rotations during angled collisions.

It is important to note that while this study tested the types of head impacts that rugby players may experience, the headgear itself was not tested. This study primarily defines the head positioning and testing that can be used to potentially simulate a rugby injury, and it can be seen in the following sections how Stitt et. al have used such headform testing to compare different brands of scrum caps. As such, the results of this review by Stitt et al., 2022 are intended to inform design choices for rugby headgear, and to inform rugby headgear testing standards by pointing out these inconsistencies.

Linear and Rotational Acceleration Injury

While Rugby players experience both linear and rotational acceleration impact to the head, it is important to look into how both metrics may cause injury. Stitt et al. 2022 compared five different scrum caps, and found that all caps reduced both peak linear acceleration (PLA) and peak rotational acceleration (PRA) on impact surfaces of 0˚, 30˚, and 45˚ at a variety of impact velocities compared to no scrum cap.[12]

Figure 5: Composite peak rotational accelerations of each headgear compared to no headgear. [12]
Figure 6: Composite peak linear accelerations of each headgear compared to no headgear.[12]

As seen in figure 5 and figure 6, two of the scrum caps: N-Pro (Labelled Headgear #4) and Gamebreaker Pro (Labelled Headgear #5) performed better than the other scrum caps, with reduced PLA and PRA across all impact surfaces and velocities. These two caps also showed reduced Head Injury Criteria (HIC) and Rotational Injury Criterion (RIC) at all head impact velocities. The study also found that the highest PLAs and PRAs occurred in different locations, with the highest PRA occurring in the Side and SR Boss impact positions (Figure 7, Row 3). This is likely because the impact force does not travel directly though the head centre of mass, and the head is instead forced to rotate about the neck. In the SR Boss position, the impact occurs towards the back of the side of the head, approximately behind the ear. The SR Boss position could not be tested for flat surface impacts, as the headform would instead impact at the RR Boss position, which is the side of the rear of the head, approximately where the parietal and occipital bones meet (Figure 7, Row 2 Right-Side). PLA and PRA were found to be reduced when impacting an angled surface, as the head travels further during the impact.

Figure 7: Impact locations and MEP pad contact area for 20 and 45 degree impact surfaces.[12]

Strain-based Brain Injury

While investigating the efficacy of rugby scrum caps at preventing both rotational and linear acceleration is an improvement from only looking at linear acceleration, rotational and linear kinematics alone are not sufficient to assess brain strain due to an impact. Stitt, et al. 2024 used deep learning brain injury models to investigate similar scrum caps to what they tested in their 2022 study, including the N-Pro and Gamebreaker Pro.[13] Their model used a publicly available pre-trained convolutional neural network (CNN) model trained on the Worcester Head Injury Model (WHIM v1.0) to estimate 3D voxel-wise maximal principal strain (MPS) over the entire brain in each head impact. This study focused on metrics associated with concussions, such as peak regional brain strain and the peak resultant rotational velocities. The N-Pro and Gamebreaker Pro (Headgears 4 and 5) were generally better than no scrum cap at reducing brain strain , as they saw a reduction in mean peak MPS by 0.12–0.13 (12–13% strain) compared to the no headgear case. The slight reduction in peak strain to the cerebrum for these two scrum caps can also be seen in Figure 8, where these two caps show the lowest median peak strain for all 4 drop heights. The other three scrum caps tested did not show a consistent reduction. This was attributed to the viscoelastic properties of the N-Pro and Gamebreaker Pro materials, as these two caps were made of a higher density foam.

Figure 8: 95% bootstrapped confidence intervals for maximum principle strain in the cerebral hemispheres. [13]

Scrum Cap Innovation

Both the N-Pro and Gamebreaker pro used viscoelastic foam, while the three other tested scrum caps used materials that are less effective in absorbing impact energy.[12] The Gamebreaker pro showed a greater  reduction in PRA compared to the N-Pro, which the study suggests is likely due to its greater thickness. However, neither the N-Pro or Gamebreaker Pro are fully approved for use by World Rugby, while the other three tested scrum caps are. The N-Pro has been approved by World Rugby for the Global Law Trial, a 5-year trial intended to “field test” new headgear materials and technology.[14] Manufacturers cannot conclusively claim that a scrum cap can reduce the risk of head injury without data from the headgear being worn in games. The Global Law Trial is intended as an avenue for manufacturers to obtain this data, which will be used by independent regulatory bodies to determine if these scrum caps are effective in reducing head injury.[15]

3.0 Problems and Controversies

Although many of the previous studies mentioned above have shown that headgear may be able to reduce the severity of head impacts during rugby, controversy in rugby headgear research lies in whether current testing and regulation standards accurately reflect on-field injury mechanisms. Studies on the topic also show considerable  variation in testing methodology, material usage, and ability for biofidelic and game-like conditions.[9][13] Current methods primarily use drop-testing, as required by World Rugby Regulation 12, which ignores many real-life variables including foam degradation, multi-directional impacts, and biofidelic neck reactions.[8][12]

Methodological Testing

Simplified Impact Kinematics

Many studies only measure linear and rotational acceleration and rotational velocity, ignoring the effects of headform geometry and mass distribution.[10] This simplification creates variability amongst research studies and manufacturers. While these simplifications allow for more consistent testing protocols, the data that is being collected does not accurately portray real-life conditions.

Incorrect Boundary Conditions

The International Rugby Board suggests that drop-test setups use heights of 30cm. It has been shown, however, that this height creates closing speeds (2.4 m/s) much slower than those observed in rugby matches (7-13.7 m/s).[9] Using impact speeds slower than that of real-game impacts could lead to inaccurate conclusions as lower accelerations wouldn’t accurately represent the amount of energy that is transferred during game impacts. It has also been shown that neck orientation and stiffness greatly affect the rotational acceleration, but most tests exclude neck assemblies or musculature influence.[13][16] Without either of these factors considered, impact methods are unable to show the impact of the head-neck relationship.

Material and Structure Considerations

Repetitive Impact Fatigue

It was stated in Knouse, et. al, 2003, players use the same headgear for entire seasons, some even multiple, however, most studies do not use repeated impact methods to replicate this.[9] It was shown that these repetitive impacts actually lead to a “memory” effect, meaning that impact performance is greatly reduced as foam cells begin to collapse.[17][18] Additionally, although there are recommendations provided by some scrum cap companies of how many months a cap can be used before replacement, a statistic or recommendation on the number of repeated impacts that the material can realistically sustain before being considered damaged could not be easily obtained.[19]

Temperature Effect

Studies have shown that elevated head temperature during game day can soften foam and affect the mechanical properties.[13][18] Above its glass transition temperature, a material is flexible, but when it cools below this point, it begins to harden. As most foams used for the rugby headgear exhibit their glass transition temperature close to laboratory room temperature and this temperature was essentially constant throughout all testing trials, temperature was not considered as a contributing variable in this study.[12]

Regulatory Gaps

Efficacy of Headgear

It has been shown through field studies that the usage of headgear does not show a statistical significant reduction in concussion incidence.[20] Many players see the usage of headgear as a threat to game integrity and adds to the tension of headgear usage regulations.

Regulations Affecting New Designs

The World Rugby Regulation 12 restricts maximum foam thickness to 10mm and density to 45 kg/m³. Laboratory evidence has shown that by increasing the foam thickness and density past the regulatory limits, the peak headform acceleration can be reduced.[13][18] Due to the increased thickness, the deceleration distance is increased, resulting in a lower peak acceleration felt at the head, due to more dissipation of energy. To stay under the thickness and density regulated values, researchers have begun testing viscoelastic materials due to their potential for providing better protection.[17]

Conclusion

Controversy in rugby headgear testing is important as it highlights the restrictions that the World Rugby Regulation 12 are putting on headgear designs. Through identifying the misrepresentation of real-life conditions in current methods, it is shown that they may reduce the development of equipment that could reduce concussive and subconcussive injury risks.

4.0 Future Research

Previous efforts have mapped out where and how rugby head impacts are sustained, quantified the performance of various scrum caps in standardized drop tests and investigated newer viscoelastic designs, as seen with the high performance of the viscoelastic N-Pro and Gamebreaker designs. Based on the combined findings, however, there are several important limitations. These limitations relate directly to experimental set up, and to the lack of evidence that connects laboratory performance to actual player behaviour. To address these problems, targeted studies based on injury mechanics need to be undertaken instead of continuing to conduct isolated drop testing.

Build a Rugby-Specific, Validated Impact and Testing Framework

There have been no games played to date that have reported patterns of impacts on where players are struck, and how their heads move in association with their necks within a match setting. The findings are that all blows are clustered to the anterior and lateral surfaces of the player's head, and that complex combinations during concussive events of translation, rotation and flexion vary at times.[21] Testing scrum caps in the laboratory has demonstrated that performance depends on test configuration: flat steel and compliant pads with or without an attached Hybrid III neck produce widely different results, as do flat compared to angled impact surfaces. Stitt et al. (2022) showed that the high performance of viscoelastic solutions like N-Pro and Gamebreaker Pro is governed by this particular configuration, whereas previous research on a standard foam cap found weaknesses from a structural standpoint in the occipital area and loss of impact attenuation behavior after multiple impacts.[12]

This field is lacking a combined, rugby-focused approach that utilises real collision data to determine the loading on which conditions scum caps are tested. Instead, future work should identify representative impact scenarios based on available match and tackle data. This data could then be directly mapped to standardized laboratory setups, considering the performance of headgears regionally (frontal, temporal, occipital) and over realistic repetitions, temperatures and ages.[22] This implementation would allow for validated test systems, where measured differences are indicative of player protection in match-relevant mechanics.

Linked Strain-Base Metrics to Clinical Relevant Outcomes

Recent research goes beyond maximum linear acceleration to include rotational kinematics and head injury criterions. Stitt et al. (2022) have also compared several commercially produced scrum caps using both peak linear acceleration (PLA) and peak rotational acceleration (PRA) as well as HIC and RIC.[12] Meanwhile, Stitt et al. (2024) utilized deep-learning-based surrogate brain models based on drop-test kinematics to approximate regional brain strain with various designs of headgear, where only certain viscoelastic systems resulted in consistent reductions.[13] Additional experimental and numerical studies on soft-shell rugby headgear have focused on the effect of material properties, thickness, construction, repetitive loading on impact attenuation. However, these aforementioned analyses were derived from simplified laboratory-generated impacts. None are based on in-game kinematic histories from instrumented players and none are validated with respect to rugby concussion incidence or cumulative sub-concussive exposure.[23]

The missing steps are the combination of three layers into a unified evidence chain: valid real match impact measures, such as instrumented mouthguards or head-worn sensors, validated finite element or trained brain models, and longitudinal clinical follow up.[24] This includes the use of actual rugby specific impact time histories as inputs to brain models, comparing predicted distributions of strain with and without particular scrum caps. From there, researchers could examine if reduction observed in practice translates into reduced diagnosed concussion rates during the high level of exposure over one or more seasons. Once this link has been established, reductions in peak acceleration or estimated strain from controlled drop tests can be meaningfully interpreted in terms of injury risk for players, and used as a more reliable basis for regulatory decisions.

When realistic rugby impact patterns, regional vulnerability, material degradation, cap fit and positioning, player behaviour, and validated brain injury metrics are considered together as one system, clinically meaningful results in injurious brain loading remains a question, regardless of the type of head protection that is used.

5.0 Citations

  1. ↑ "Cauliflower Ear: What It Is, Causes & Treatment". Cleveland Clinic. Retrieved November 5, 2025.
  2. ↑ "Scrum Caps Explained: What are rugby players wearing on their heads". September 17, 2023. Retrieved November 5, 2025.
  3. ↑ 3.0 3.1 Richardson, Jordan; Stanbouly, Dani; Moynihan, Harrison; Renyolds, Renee M.; Recker, Matthew J.; Markiewicz, Michael R. (January 13, 2022). "The Most Dangerous Game: A Review of Head and Neck Injuries in American Football and Rugby". Craniomaxillofacial Trauma and Reconstruction. 16: 15–22.
  4. ↑ Cooke, Robert; Strang, Matthew; Lowe, Richard; Jain, Neil (June 2022). "The Epidemiology of Head Injuries at 2019". The Physician and Sportsmedicine. 51 (4): 1–7.
  5. ↑ Winter, John. "Do Rugby Players Wear Cups? (Explained)". Rugby World. Retrieved November 5, 2025.
  6. ↑ 6.0 6.1 "Approved Equipment". World Rugby. Retrieved November 5, 2025.
  7. ↑ Oliver, L (April 22, 2025). "The Ultimate Guide to Rugby Scrum Caps". Rugby Stuff. Retrieved November 5, 2025.
  8. ↑ 8.0 8.1 McIntosh, Andrew S.; McCrory, Paul; Comerford, John (December 2000). "The Dynamics of Concussive Head Impacts in Rugby and Australian Rules Football". Medicine and Science in Sports and Exercise. 32 (12): 1980–1984.
  9. ↑ 9.0 9.1 9.2 9.3 9.4 9.5 Knouse, Carissa L; E Gould, Trenton; Caswell, Shane V; Deivert, Richard G (2003). "Efficacy of Rugby Headgear in Attenuating Repetitive Linear Impact Forces". Journal of Athletic Training. 38 (4): 330.
  10. ↑ 10.0 10.1 10.2 10.3 10.4 10.5 10.6 Stitt, Danyon; Kabaliuk, Natalia; Alexander, Keith; Draper, Nick (August 24, 2022). "Drop Test Kinematics Using Varied Impact Surfaces and Head/Neck Configurations for Rugby Headgear Testing". Annals of Biomedical Engineerings. 50 (11): 1633–1647.
  11. ↑ "MEP pad". Cadex Inc. July 18, 2025. Retrieved November 10, 2025.
  12. ↑ 12.0 12.1 12.2 12.3 12.4 12.5 12.6 12.7 12.8 Stittt, Daynon; Kabaliuk, Natalia; Alexander, Keith; Draper, Nick (January 20, 2022). "Potential of Soft-Shell Rugby Headgear to Mitigate Linear and Rotational Peak Accelerations". Annals of Biomedical Engineering. 50 (11): 1546–1564.
  13. ↑ 13.0 13.1 13.2 13.3 13.4 13.5 13.6 Stitt, Danyon; Kabaliuk, Natalia; Alexander, Keith; Draper, Nick (September 27, 2024). "Potential of Soft-Shelled Rugby Headgear to Lower Regional Brain Strain Metrics During Standard Drop Tests". Sports Medicine - Open. 10.
  14. ↑ "N-Pro and World Rugby Launch The First Ever Global Law Trial For Rugby Headgear". November 19, 2019. Retrieved November 15, 2025.
  15. ↑ "Law 4 Headgear Trial Terms and Conditions". World Rugby. Retrieved November 10, 2025.
  16. ↑ Seminati, Elena; Cazzola, Dario; Trewartha, Grant; Williams, Sean; Preatoni, Ezio. "BIOMECHANICAL LOADS IN RUGBY UNION TACKLING ARE AFFECTED BY TACKLE DIRECTION AND IMPACT SHOULDER". International Society of Biomechanics in Sports Proceedings Archive. 35 (1).
  17. ↑ 17.0 17.1 Ganly, Mark; McMahon, Jill Mary (December 7, 2018). "New generation of headgear for rugby: impact reduction of linear and rotational forces by a viscoelastic material-based rugby head guard". BMJ Open Sport Exercise Medicine. 4 (1).
  18. ↑ 18.0 18.1 18.2 McIntosh, Andrew S; McCrory, Paul (October 1, 2000). "Impact energy attenuation performance of football headgear". British Journal of Sports Medicine. 34: 337–341.
  19. ↑ "N-Pro Frequently Asked Questions". N-Pro. Retrieved November 20, 2025.
  20. ↑ McIntosh, Andrew; McCrory, Paul; Finch, Caroline F.; Best, John P.; Chalmers, David J.; Wolfe, Rory (February 2009). "Does Padded Headgear Prevent Head Injury in Rugby Union Football?". Medicine & Science in Sports & Exercise. 41 (2): 306–313.
  21. ↑ King, Doug; Hume, Patria A.; Gissane, Conor (December 20, 2014). "Instrumented Mouthguard Acceleration Analyses for Head Impacts in Amateur Rugby Union Players Over a Season of Matches". American Journal of Sports Medicine. 43 (3): 614–624.
  22. ↑ Jones, Ben; Weaving, Dan; Till, Kevin; Owen, Cameron; Begonia, Mark; Stokes, Keith A; Rowson, Steven; Phillips, Gemma. Hendricks, Sharief; Falvey, Eanna C.; Al-Dawoud, Marwan; Tierney, Gregory;. "Ready for impact? A validity and feasibility study of instrumented mouthguards (iMGs)". British Journal of Sports Medicine. 56 (20). |first2= missing |last2= (help)CS1 maint: extra punctuation (link)
  23. ↑ Henley, Stefan; Andrews, Kathryn; Kabaliuk, Natalia; Draper, Nick (March 26, 2023). "Soft-shell headgear in rugby union: a systematic review of published studies". Sports Sciences for Health. 19: 765–782.
  24. ↑ Ng, Laurel J.; Volman, Vladislav; Gibbons, Melissa M.; Phohomsiri, Pi; Cui, Jianxia; Swenson, Darrell J.; Stuhmiller, James H. (June 14, 2017). "A Mechanistic End-to-End Concussion Model That Translates Head Kinematics to Neurologic Injury". Frontiers in Neurology. 8 (269).
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