Context: Poor core stability is believed to increase vulnerability to uncontrolled joint displacements throughout the kinetic chain between the foot and the lumbar spine.Objective: To assess the value of preparticipation measurements as predictors of core or lower extremity strains or sprains in collegiate football players.Design: Cohort study. Setting: National Collegiate Athletic Association Division I Football Championship Subdivision football program.Patients or Other Participants: All team members who were present for a mandatory physical examination on the day before preseason practice sessions began (n 5 83).Main Outcome Measure(s): Preparticipation administration of surveys to assess low back, knee, and ankle function; documentation of knee and ankle injury history; determination of body mass index; 4 different assessments of core muscle endurance; and measurement of step-test recovery heart rate. All injuries were documented throughout the preseason practice period and 11-game season. Receiver operating characteristic analysis and logistic regression analysis were used to identify dichotomized predictive factors that best discriminated injured from uninjured status. The 75th and 50th percentiles were evaluated as alternative cutpoints for dichotomization of injury predictors.Results: Players with $2 of 3 potentially modifiable risk factors related to core function had 2 times greater risk for injury than those with ,2 factors (95% confidence interval 5 1.27, 4.22), and adding a high level of exposure to game conditions increased the injury risk to 3 times greater (95% confidence interval 5 1.95, 4.98). Prediction models that used the 75th and 50th percentile cutpoints yielded results that were very similar to those for the model that used receiver operating characteristic-derived cutpoints.Conclusions: Low back dysfunction and suboptimal endurance of the core musculature appear to be important modifiable football injury risk factors that can be identified on preparticipation screening. These predictors need to be assessed in a prospective manner with a larger sample of collegiate football players.Key Words: clinical prediction rule, injury prevention, injury risk, core stability Key Points N Low back dysfunction and poor endurance of the core musculature appear to be modifiable injury risk factors for preventing core and lower extremity injuries in collegiate football players.N These factors can be identified by preparticipation screening and individualized core stability training regimens implemented to potentially reduce the risk of core and lower extremity injuries in this population.