Summers, KM, Snodgrass, SJ, and Callister, R. Predictors of calf cramping in rugby league. J Strength Cond Res 28(3): 774–783, 2014—Exercise-associated muscle cramps (EAMC) in the calf are common in rugby league. To date, the etiology and predictors of calf cramping are poorly understood. The aim of this study was to undertake a prospective investigation to identify predictors of calf cramping in rugby league players. Demographic and anthropometric data and calf cramp and injury history were collected in the preseason. Hydration status, number of games played, and calf cramps were recorded on game days. Male rugby league players (n = 103, mean age 18.8 ± 4.1 years) were classified as either EAMC (experienced at least 1 incident of calf cramps in the season) or no EAMC (no calf cramps). The following were investigated as possible predictors of EAMC using logistic regression modeling: competition level, age, ethnicity, playing position, history of cramping, precramping, low back pain, foot orthotic usage, foot posture, foot strike, muscle flexibility, calf girth, hydration status, and number of games played. Half the players, n = 52, experienced at least 1 incidence of calf cramping. Playing in a senior competition level (odds ratio: 0.21; 95% confidence interval: 0.06–0.75; p = 0.016), a history of calf cramping (10.85; 2.16–54.44; p = 0.004), and a history of low back pain resulting in missed field minutes (4.50, 1.37–14.79; p = 0.013) were found to predict EAMC. This study suggests that there is a high incidence of calf cramping in rugby league, especially at senior competition levels, and supports preseason screening in senior players to idetify those at risk of calf cramping and the development of possible preventative strategies.