Who Is Keeping Score: The Effect of a Mercy Rule on Head Impact Rates in Canadian High School Tackle Football Games.

OBJECTIVE

To examine the association between the Mercy Rule (MR) and head impact incidence rates (IRs) in Canadian high school football games.

DESIGN

Cross-sectional.

SETTING

Calgary, Canada.

PARTICIPANTS

Two high school football teams (ages 15-16 years) had a total of 16 team-games videorecorded and analyzed.

INTERVENTIONS: The MR mandates continuous running time in the second half of games when the score differential is 35 points or greater.

MAIN OUTCOME MEASURES: Head impact IRs and incidence rate ratios (IRRs) were used to compare head impact rates in MR and non-MR games.

RESULTS

Mercy Rule games had 28% fewer plays, and the head impact IR per team-game was 27% lower [IRR, 0.73; 95% confidence interval (CI), 0.61-0.89] in MR games (IR, 241.67; 95% CI, 199.24, 293.13) than in non-MR games (IR, 328.91; 95% CI, 313.04, 345.57). Across all games (MR and non-MR), running plays accounted for more than half of all head impacts, and the head impact rates for running plays exceeded all other play types except for a sack of the quarterback. Players engaged in blocks (blocking or being blocked) accounted for 68.90% of all recorded head impacts. The highest proportion of impacts involved the front of the helmet (54.85%). There was no difference in head impact rates by player-play comparing MR and non-MR games (IRR, 1.01; 95% CI, 0.85, 1.19).

CONCLUSIONS

Given the concerns for potential long-term consequences of repetitive head impacts, the MR is a prevention strategy by which head impact rates can be significantly lowered when a significant score differential exists.