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

Abstract

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.