In this study, we used a laboratory-calibrated impact monitoring mouthguard (IMM) system and video review to document the presence of 77 potential blunt and inertial head impacts across 291 athlete exposures in ice hockey players aged 14 to 18. Our rate of impacts per athlete exposure was one to two orders of magnitude lower than prior studies, and we did not measure any high gravity impacts in the range 100 g to 200 g. We found four cases where the athlete sustained a “No-Go” impact per the National Football League (NFL) video review criteria. The No-Go cases were of similar impact dose severity and direction with No-Go athletes in American football and combat sport. We also measured a high-energy frontal impact dose that resulted in no visible impairment, and this also was on par with visibly normal athletes in American football and combat sport studied previously. The inertial and blunt impact time trace data collected in this study give a full six-degrees-of-freedom kinematic profile of true ice hockey head impacts measured in the “living laboratory.” This detailed knowledge, for the first time, permits creation of helmet tests per the on-ice exposures where designs can acutely focus on reducing impact energy dose. Assuming skull fracture risks have been sufficiently minimized, reduction of energy transfer to the brain in side and rear impacts should be the paramount design considerations. We suggest that for players to be monitored using a mouthguard-based system, coaches and referees must enforce current safety rules on mouthguard use during play. Stringent enforcement of rules against checking from behind would help further reduce instances of the already rare No-Go impacts. And while relatively few impacts occurred in our ice hockey population, it would be prudent to investigate effects of cumulative impact dosing in a broader set of athletes longitudinally.