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The purpose of this study was to quantify the between-session reliability of time, velocity, and distance measures over 54.7 m straight-line and home-to-second base sprints (curvilinear), using global positioning satellite (GPS) technology. Twelve trained male high school baseball position players attended four sessions: one familiarization session and three identical testing sessions, separated by at least two days, each consisting of two linear and two curvilinear trials. There was no statistically significant evidence (p < 0.05) of systematic change in any of the variables between sessions, with the majority of the mean percent changes ranging from −2.7 to 2.5%, and only four between-session comparisons greater than 2% (−6.2 to 3.4%). In terms of absolute consistency, no measure exceeded a coefficient of variation (CV) of 10%, with the majority (93%) of the CVs under 5%. With regard to relative consistency, 66% of the measures had intraclass correlation coefficients (ICCs) greater than 0.74, ranging from 0.76 to 0.98. Comparison of smallest worthwhile change (SWC) values with CV-derived typical error indicated that several key time- and speed-based metrics were sensitive to meaningful performance changes, with error estimates that were comparable to or smaller than SWC. In contrast, event-timed typical errors (e.g., time to peak speed) were substantially greater than the SWC, indicating limited sensitivity for detecting small performance changes. The non-significant changes in the mean, low CVs, and high ICCs, for the most part, over repeated testing occasions, indicate acceptable between-session reliability for many of the procedures and GPS-derived variables examined in this study. Practitioners should prioritize linear time at 41.1 m and 54.7 m and velocity at 27.4 m and 41.1 m for return-to-play and short-term performance tracking. For curvilinear running, peak speed before first base, peak speed before second base and after first base, and speed at 41.1 m are the most suitable monitoring metrics based on the results. Specifically, speed at 41.1 m should be considered for return-to-play and short-term performance tracking, while peak speed before first base and peak speed before second base and after first base may be used cautiously when larger performance changes are expected.