Concussions in the National Football League: the evolution of video review for assessing the frequency and reliability of visible signs.

: The use of video review to document visible signs (VS) of sport-related concussion in the National Football League (NFL) is a novel method to recognize head injuries. : The current pilot studies used varying methodologies to (1) examine the frequency of VS in concussed NFL players using the Australian Football League's (AFL) checklist, and (2) assess the reliability of VS between non-expert and expert raters. : Cohort study : In the first pilot study, two rated VS of SRC occurring in the 2015 NFL season (96) using a single VS from the AFL checklist.