Observable player behaviours and playing performance following helmet strikes in elite cricket

Introduction

Head impacts occur in elite cricket at a rate of 7.2 per 1000 player days with concussions occurring at 2.3 per 1000 player days. Although the risk of both is not uniformly spread through the team, this equates to one player receiving a head impact every 12 days of play and a concussion every 36 days of play, per team.1

These injuries are a source of concern. Partly, this relates to research linking concussive head injuries to long-term psychiatric and neurodegenerative disease, although Jones et al2 reported no increased risk of dementia in retired professional cricketers. However, there is also the potential for impaired playing performance, increased musculoskeletal injury risk and, in elite sport, limitation of career length and earning potential in the short- and medium-term following concussion.3–7

There are also concerns around repetitive ‘sub-concussive’ impacts and the potential for these accumulated impacts to be as important in the short- and long-term brain health of athletes.8–10

Improved understanding of head impact injuries in cricket is important, particularly given approximately 70% of concussions occurring after such injuries are not diagnosed at the time of the strike. Possibly, this may be because the ‘traditional’ observable features signifying transient loss of consciousness seen after concussion in other sporting codes are not common in the elite cricket setting.1 11

Thus, our objective was to investigate helmet strikes occurring in elite English cricket from two perspectives, to inform the detection of significant strikes and the aftercare of players suffering them. First, to describe the observable player behaviours seen on video review following helmet strike and analyse any differences seen between players subsequently diagnosed with concussion versus those in whom concussion is excluded. Second, to describe effects on playing performance following helmet strike and, again, differences seen based on concussion diagnosis.

Methods

Video analysis

The ECB ISO collated all available videos of helmet strikes at First-Class County teams (across County Championship, One Day 50 Over and T20 cricket) and the men’s senior national side from each team’s Performance Analyst. A selection of these videos was reviewed by the ISO and the lead author to identify visible features that may be relevant to investigate further in the entire cohort of videos.

This review was made with reference to the Berlin Consensus Statement, the concussion protocols of the ICC, World Rugby, FIFA and the consensus statement on video features of concussion. This produced a list of 19 signs the player may display and three variables relating to the impact location and subsequent direction of the ball (figures 1 and 2).

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Figure 1

Illustration of location on the helmet of the ball impact. Key: 1. frontal (helmet shell / badge area); 2. peak; 3. peak and grill; 4. grill; 5. temple region; 6. occiput; 7. crown.

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Figure 2

Illustration of the direction of ball travel following helmet strike.

The ball directions were coded as red, yellow and green corresponding to the theoretical transfer of energy in each. For example, if the ball strikes the helmet and continues behind the batsman, this is likely to represent a glancing blow (green) as compared with the ball striking the helmet and travelling directly back down the pitch (red). This list was reviewed by three experienced ECB doctors with only minor changes suggested.4 11 13–16 The final list is included in online supplemental appendix 1.

All videos were then reviewed and coded by two researchers. Any discrepancies were discussed and if consensus could not be reached, the senior author was consulted. The mean of the two transverse plane ball angles was calculated.

Results

194 male senior players, registered to compete in the ECB domestic First-Class County Championship from 2016 to 2018 inclusive, received a helmet strike, 56 HS-C and 153 HS-NC.

Performance analysis

Batting performance

Adequate batting performance data were available for 24 of the 56 HS-C group and 138 of the 153 HS-NC group. Performance data were not available for each player for each time period. A summary of the available data is shown in table 1, with the individual raw batting averages for each group in online supplemental tables 1 and 2.

Table 1

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Summary of the number of players with available batting and bowling performance data points, following helmet strike for each time period between the HS-C and HS-NC groups

The mean, within-individual, batting performance z-scores for the HS-C group increased from 2-year pre-helmet strike to 1-month post-RTP before decreasing between 1-month post and 3-month post-RTP (figure 3). In the HS-NC group, mean within-individual performance decreased from 2-year pre to 1-month post incident and then decreased further from 1-month to 3-month post incident (figure 3).

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Figure 3

Mean within-individual performance z-scores for 2 years pre-helmet strike to 1 and 3 month post return to play for batting (A) and bowling (B).

For the HS-C group, the assumption of normality was not met (W=0.88, p≤0.001), and no difference in batting performance was seen between the three time periods (H(2)=1.58, p=0.45).

For the HS-NC group, the assumption of normality was also not met (W=0.88, p=<0.001). A difference in batting performance was seen between the three time periods (H(2)=21.48, p<0.001). Post hoc tests were conducted using Wilcoxon rank sum tests and found differences in batting performance with a small effect for 2 years pre and 1 month post (p<0.05, r=0.17) and a moderate effect for 2 years pre to 3 months post (p<0.001, r=0.31). No differences were found between 1 and 3 months post-RTP (p=0.16, r=0.09).

Therefore, following a HS-NC, there was a reduction in batting average from 2 years pre incident (mean=0.24±0.75) to 1 month post (mean=−0.06±0.83) with a continued reduction in batting performance 3 months post incident (mean=−0.24±0.70).

Bowling performance

Adequate data for bowling performance were available for 12 of the HS-C group and 58 of the HS-NC group. A summary of the available data is provided in table 1, with the individual raw bowling averages for each group in online supplemental tables 3 and 4.

The mean within-individual bowling performance z-scores for the HS-C group followed a similar pattern to the batting performance, increasing from 2-year pre-helmet strike to 1-month post-RTP before decreasing from 1-month to 3-month post-RTP (figure 3). For those in the HS-NC group, mean within-individual bowling performance z-scores decreased from 2 years pre to 1 month post before recovering slightly from 1 month to 3 months post but still down from their performance 2 years pre (figure 3).

For the HS-C group, the assumption of normality was not met (W=0.80, p=<0.001), and no difference in bowling performance between the three time periods was seen (H(2)=3.00, p=0.22). Similarly, for HS-NC group, the assumption of normality was not met (W=0.88, p=<0.001), and no difference in bowling performance between the three time periods was seen (H(2)=3.04, p=0.22).

Discussion

We have attempted to describe head impact injuries in elite cricket from the perspective of both their observable characteristics and their impacts on player performance in the context of concussive and ‘subconcussive’ injuries.

These findings indicate a non-significant trend towards initial increased batting and bowling performance at 1-month poststrike, following by a decline in performance at 3 months poststrike in those who suffer a helmet strike with concussion. This is consistent with findings from elite baseball by Sabesan et al,18 which showed a non-significant decline in batting and pitching performance on RTP postconcussion. However, this contrasts with Wasserman et al’s19 work in the same population. They demonstrated a significant reduction in batting performance in the initial 2 weeks post-RTP, with a non-significant reduction at 4–6 weeks.18 19

Studies on playing performance in other sports postconcussion, however, provide similarly inconsistent results, even within the same sport. A possible explanation for this may be the management of RTP following concussion. In elite soccer, Ramkumar et al7 demonstrated that players returning through more aggressive protocols suffered a decrement in performance versus those managed more conservatively.

Crucially, however, a significant reduction in batting performance was seen following a helmet strike, which did not result in concussion at both 1 and 3 months. While reductions in motor control have been described following subconcussive impacts in boxers, the effect of such impacts on ‘real-world’ sports performance is not well studied.20

Possibly, this may reflect concussions, which are not detected under the current approach to diagnosis. Alternatively, the differences seen between the HS-C and HS-NC groups may be explained by the extended period of rest and graded recovery afforded by the concussion diagnosis. Whether this acts to ameliorate a lasting effect on neurocognitive/motor performance or an independent effect on player psychology and behaviour should also be considered. This is important to investigate further as it may highlight a need for further assessment of these players and a managed RTP, even in the absence of concussion.

Our findings also suggest that helmet strikes occurring to the frontal, peak and grill sections of the helmet represent the greatest relative risk in terms of subsequent diagnosis of concussion. This contrasts with accelerometry and modelling data from other helmeted and non-helmeted sports that suggest lateral impacts are more injurious.21–23 In cricket, where the bowling line is permitted to contact the batsman who must react, impacts to the front of the helmet may result from a faster ball speed while a slower ball on a similar trajectory may prompt a player to turn their head in preparation for an impact. However, this relationship is clearly complex, as demonstrated by Saw et al,24 who’s work highlighted that impacts to the back of the helmet carried the highest positive predictive value of concussion.

Alternatively, the combination of helmet strike location and the subsequent direction of ball travel could be important. Counter to our intuitive colour-coding zones, impacts in the Yellow zone represented the largest concussion risk. This may be because, when the ball strikes the frontal section and rebounds laterally (Yellow zone), the rotational force on the head is greater. Rotational, rather than translational, impacts are theorised to be more likely to result in concussion. This also raises a question about whether neck strengthening interventions may be beneficial for primary prevention.24 25

Green zone impacts were also found to have higher concussion risk than expected, however, our suspicion is that this represents difficulties in judging the flight of the ball in the frontal plane. Frequently, only one view was available, usually in the frontal plane and often too narrow to view the landing of the ball after rebound. Therefore, travel into the green zone on the frontal view may in fact appear in the red zone in the sagittal view, suggesting diagnosis could be improved with access to multiple angles. This is supported by the findings of Saw et al24 who conducted a similar exercise in Australian cricket and demonstrated that the rebound of the ball towards the source or the ball stopping dead was associated with a higher risk of concussion. Standardisation of the views and reference frame in future may assist in investigating this further.

The ECB requires all players to undergo annual baseline testing using the Standardized Concussion Assessment Tool 5 and Immediate Post-Concussion Assessment and Cognitve Test (ImPACT) (ImPACT Applications, Coralville) on a biannual basis unless helmet strikes are recorded, in which case it is annual. This data suggest that more detailed ImPACT testing should continue and that annual reviews should be considered. Jones et al2 surveyed retired cricketers for long-term health outcomes. No cases of dementia/neurocognitive disease were recorded, but ongoing review of retired cricketers and any potential consequence of long-term helmet strikes is warranted.

Notably, observable signs of concussion in this context appear different to those from other field sports. The value of video replay in detecting concussion is clear, particularly in football codes, and the features, which suggest a transient loss of consciousness or a concussion, are well documented. However, none of those features appeared in this series and their absence may make concussion diagnosis more challenging in cricket if this is not recognised.1 11 15 26 27

Features suggesting motor incoordination were valuable in detecting concussion in this study. However, features indicating urgency and concern from other players or officials as well as the player inspecting their helmet and pausing for >4 s before the next delivery were also important. These may be unique to cricket where rules and culture dictate the action pauses until the batsman is ready.

These findings suggest several areas for further investigation, both to understand their implications and to improve player safety. However, some important limitations should be recognised. First, our groups were weighted towards HS-NC. As a result, the concussive helmet strike element of the performance analysis was underpowered, which may explain the lack of significant findings in this group. This was unavoidable in view of the low incidence of concussive helmet strikes in cricket; however, it is an important caveat. In addition, we excluded from our analysis head impacts occurring to fielding or bowling players. This was due to the low total number of these incidents, all of them resulting in concussion. Finally, we were not able to analyse differences in the clinical status of the player between those helmet strikes captured on video and those which could not be reviewed, which may introduce a potential source of bias, though we feel this is unlikely.

Conclusion

Helmet strikes are common in elite cricket. While the rate of concussion following helmet strike is low, these findings suggest that HS-NC may be more important than previously thought and may require management involving a supported RTP. For example, involving consideration of and interventions directed at visual motor speed and psychological readiness. The video features of helmet strikes, which may point to concussion, appear to differ in cricket when compared with other sports and this requires further investigation and dissemination to ensure that medical staff are able to recognise key features in the cricket context.