Aim To determine whether the King–Devick (K–D) test used as a sideline test in junior rugby league players over 12 matches in a domestic competition season could identify witnessed and incidentally identified episodes of concussion.

Methods A prospective observational cohort study of a club level junior rugby league team (n = 19) during the 2014 New Zealand competition season involved every player completing two pre-competition season baseline trials of the K–D test. Players removed from match participation, or who reported any signs or symptoms of concussion were assessed on the sideline with the K–D test and referred for further medical assessment. Players with a pre- to post-match K–D test difference > 3 s were referred for physician evaluation.

Results The baseline test–retest reliability of the K–D test was high (rs = 0.86; p < 0.0001). Seven concussions were medically identified in six players who recorded pre- to post-match K–D test times greater than 3 s (mean change of 7.4 s). Post-season testing of players demonstrated improvement of K–D time scores consistent with learning effects of using the K–D test (67.7 s vs. 62.2 s).

Discussion Although no witnessed concussions occurred during rugby play, six players recorded pre- to post-match changes with a mean delay of 4 s resulting in seven concussions being subsequently confirmed post-match by health practitioners. All players were medically managed for a return to sports participation.

Conclusion The K–D test was quickly and easily administered making it a practical sideline tool as part of the continuum of concussion assessment tools for junior rugby league players.