Head impact characteristics within each cohort per year of play using impacts derived from the HITS data.

Unclear: some impact characteristics (i.e., external source, play type) were unable to be derived because they were unviewable (e.g., a heap of players); unviewable characteristics were recorded as unclear. a N = 17 players sustained impacts; n = 3 played and did not sustain any impacts. b N = 14 players sustained impacts. c N = 10 players sustained impacts; n = 1 played and did not sustain any impacts. d N = 19 players sustained impacts; n = 1 played and did not sustain any impacts. e N = 11 players sustained impacts; n = 2 players were on the team but did not play; n = 1 played and did not sustain any impacts. f N = 12 players sustained impacts; n = 1 player was on the team but did not play. (DOCX)