Background Video analyses reveal that the rate of incidents with a propensity for injury caused by opponent-to-player contact has increased by about 50% from 2000 to 2010 in Norwegian male professional football. The aim of the study was to assess whether a stricter interpretation of the Laws of the Game (red cards for high elbows in heading duels and for late/two foot tackles) could reduce the potential for injuries in Norwegian male professional football.

Methods A preintervention/postintervention design was employed, where the rate of incidents and injuries from the 2010 season (pre) was compared to the 2011 season (post). An incident was recorded if the match was interrupted by the referee, and the player lay down for more than 15 s, and appeared to be in pain or received medical treatment. Time-loss injuries were recorded by the medical staff of each club.

Results A total of 1421 contact incidents were identified, corresponding to a rate of 92.7 (95% CI 86.0 to 99.4) in the 2010 season and 86.6 (95% CI 80.3 to 99.4) in the 2011 season, with no difference between the two season. We found a reduction in the incidence of total head incidents (rate ratio (RR) 0.81, 95% CI 0.67 to 0.99), and head-incidents caused by arm-to-head contact (RR 0.72, 95% CI 0.54 to 0.97). We found no difference in tackling characteristics or contact injury rate.

Conclusions We found no significant differences in the overall rate of incidents after the introduction of stricter rule enforcement. However, the rate of head and arm-to head incidents was lower in the 2011 season.