Context: High loads in the elbow during baseball pitching can lead to serious injuries, including injuries to the ulnar collateral ligament. These injuries have substantial implications for individual pitchers and their teams, especially at the professional level of competition. With a trend toward increased ball velocity in professional baseball, controversy still exists regarding the strength of the relationship between ball velocity and elbow-varus torque. Objective: To examine the relationship between fastball velocity and elbow-varus torque in professional pitchers using between- and within-subjects statistical analyses. Design: Cross-sectional study. Setting: Motion-analysis laboratory. Patients or Other Participants: Using the previously collected biomechanical data of 452 professional baseball pitchers, we performed a retrospective analysis of the 64 pitchers (52 right-hand dominant, 12 left-hand dominant; age ¼ 21.8 6 2.0 years, height ¼ 1.90 6 0.05 m, mass ¼ 94.6 6 7.8 kg) with fastball velocity distributions that enabled between- and within-subjects statistical analyses. Main Outcome Measure(s): We measured ball velocity using a radar gun and 3-dimensional motion data using a 12-camera automated motion-capture system sampling at 240 Hz. We calculated elbow-varus torque using inverse-dynamics techniques and then analyzed the relationship between ball velocity and elbow torque using both a simple linear regression model and a mixed linear model with random intercepts. Results: The between-subjects analyses displayed a weak positive association between ball velocity and elbow-varus torque (R 2 ¼ 0.076, P ¼ .03). The within-subjects analyses showed a considerably stronger positive association (R 2 ¼ 0.957, P, .001). Conclusions: When comparing 2 professional baseball pitchers, higher velocity may not necessarily indicate higher elbow-varus torque due to the confounding effects of pitcher-specific differences (eg, detailed anthropometrics and pitching mechanics). However, within an individual pitcher, higher ball velocity was strongly associated with higher elbow-varus torque.