The CHIRPP database (1990-2009) was searched for individuals 5-19 years old who presented with a brain injury ("minor closed head injury", "concussion", "intracranial injury") while participating in ice hockey (hockey), soccer, American football (football), basketball, baseball, or rugby. Ringette and lacrosse were excluded because of the paucity of players and brain injuries. The extracted variables included age, sex, year, team sport, treatment (admitted/non-admitted), context (informal versus organized), a narrative description of the injury mechanism, and postal code. Sport context was categorized by organized and informal sport. Informal sport was defined as sport that was not regulated by third-party individuals including referees, coaches, or teachers. In contrast, organized sport was defined as sport in a setting in which formal regulation by a referee, coach, or teacher was present. Postal codes were used to determine community type (rural versus urban). Specific mechanisms of injury codes were developed by two research assistants (e.g.; "checked into boards from behind" or "hit by pitch while batting"). The specific mechanism of injury was then coded for the first 200 cases for each sport independently by the two research assistants using the developed coding list based on the narrative descriptions provided for each case. After establishing inter-coder agreement, the two research assistants applied the resulting codes to the remaining cases. Once coding was complete, proportions of injuries attributable to the specific mechanistic codes were determined. These specific mechanistic codes were also categorized into one of five categories: 'struck by player', 'struck by object' (in the environment i.e., net, post), 'struck by sport implement' (i.e., ball, stick), 'struck (playing) surface', and 'other'.
A descriptive analysis was conducted where normally distributed continuous variables were presented as means and standard deviations and dichotomous and polychotomous variables presented as proportions with associated 95% confidence intervals. A chi-square test was performed to determine if there was an association between community type and sport context. Results were stratified by sport, sex, age group (5-9, 10-14, and 15-19 years), and helmet use. Helmet use data was analyzed for ice hockey, football, and baseball. Inter-coder reliability was evaluated by calculating chance-corrected Cohen's Kappa values.