Slowed reaction time (RT) represents both a risk factor for and a consequence of sport concussion. The purpose of this study was to determine the reliability and criterion validity of a novel clinical test of simple and complex RT, called RT(clin), in contact sport athletes. Both tasks were adapted from the well-known ruler drop test of RT and involve manually grasping a falling vertical shaft upon its release, with the complex task employing a go/no-go paradigm based on a light cue. In 46 healthy contact sport athletes (24 men; M = 16.3 yr., SD = 5.0; 22 women: M age = 15.0 yr., SD = 4.0) whose sports included soccer, ice hockey, American football, martial arts, wrestling, and lacrosse, the latency and accuracy of simple and complex RT(clin) had acceptable test-retest and inter-rater reliabilities and correlated with a computerized criterion standard, the Axon Computerized Cognitive Assessment Tool. Medium to large effect sizes were found. The novel RT(clin) tests have acceptable reliability and criterion validity for clinical use and hold promise as concussion assessment tools.