Video surveillance and detection of players with visible signs of concussion by experienced medical staff facilitates rapid on-field screening of suspected concussion in professional sports. This method, however has not been validated in community sports where video footage is unavailable. This study aimed to explore the utility of visible signs of concussion to identify players with decrements in performance on concussion screening measures. In this observational prospective cohort study, personnel with basic training observed live matches across a season (60 matches) of community male and female Australian football for signs of concussion outlined in the community-based Head Injury Assessment form (HIAf). Players identified to have positive signs of concussion (CoSign+) following an impact were compared with players without signs (CoSign-). Outcome measures, the Sport Concussion Assessment Tool (SCAT3) and Cogstate, were administered at baseline and post-match. CoSign+ (n = 22) and CoSign- (n = 61) groups were similar with respect to age, sex, education, baseline mood, and medical history. CoSign+ players exhibited worse orientation, concentration, and recall, and slower reaction time in attention and working memory tasks. Comparing individual change from baseline to post-match assessment revealed 100% (95% confidence interval [CI]: 84-100%) of CoSign+ players demonstrated clinically significant deficits on SCAT3 or Cogstate tasks, compared with 59% (95% CI: 46-71%) of CoSign- players. All CoSign+ players observed to have a blank/vacant look demonstrated clinically significant decline on the Standardized Assessment of Concussion (SAC). Detection of visible signs of concussion represents a rapid, real-time method for screening players suspected of concussion in community sports where video technology and medical personnel are rarely present. Consistent with community guidelines, it is recommended that all CoSign+ players be immediately removed from play for further concussion screening.