Nearly a third of concussions in professional American football are due to impacts to the facemask, however facemask designs have remained mostly unchanged over the past decade. Head acceleration sensors in live sport provide data to potentially guide improvements in design. During the 2019-2022 seasons, 98 players from the NFL were equipped with instrumented mouthpieces that measured six degrees-of-freedom head kinematics. A total of 5104 head acceleration events (HAEs) were collected during 115 player-seasons. Datasets corresponding to the most severe HAEs were generated for the >90th percentile HARM, peak angular acceleration (PAA), and peak linear acceleration (PLA). Facemask impacts represent 59% of the >90th percentile HARM sample, with the proportion varying by position group:​ linemen (66%), hybrid (56%), speed (46%). Similar findings were observed for PLA and PAA. Facemask impacts were primarily due to contact with the helmet shell of the collision partner, with positional variance:​ linemen (49%), hybrid (43%), speed (33%). This decrease in the hybrid and speed groups was offset primarily by increased impacts to the shoulder of the impact partner. Given the high prevalence of facemask impacts in this sample, future work should be directed towards interventions that reduce the frequency and magnitude of these impacts, including improvement in facemask design and changes to player techniques and rules that mitigate facemask contact.