The purpose of this study was to provide a longitudinal profile of pitching performance in a cohort of pitchers over two collegiate seasons and a summer league. Thus, this study utilized a longitudinal design to evaluate the impact of summer league participation on subsequent collegiate regular season pitching performance. Specifically, the performance of a cohort of Division 1 collegiate baseball pitchers during the 2018 Spring collegiate season, 2018 Summer League season, and the 2019 Spring collegiate season was evaluated and stratified by pitcher designation, arm dominance, and academic status. Analyses of variance were used to identify main and interaction effects on pitching outcomes. The level of statistical significance was set at p < .05 for all analyses. Data were publicly accessed from thirty-seven Division I collegiate baseball pitchers who participated in a summer baseball league. Collectively, all pitchers significantly improved earned run average (p = .024), number of strikeouts (p = .011), and strikeout efficiency (p = .034) from 2018 to 2019 collegiate seasons. Whereas, starting pitchers (n = 15) yielded fewer earned runs (p = .039) and enhanced hit efficiency (p = .012) from 2018 to 2019 collegiate seasons. Relief pitchers (n = 16) produced significantly more strikeouts from 2018 to 2019 collegiate seasons (p = .012). Finally, there were no differences in pitching outcomes for closers (n = 6) over time (p > .05). Regarding arm dominance, right-handed pitchers (n = 23) improved win average (p = .001), strikeouts (p = .008) and strikeout efficiency (p = .031) from 2018 to 2019 collegiate seasons. Left-handed pitchers (n = 14) significantly improved earned run average (p = .015), earned runs (p = .048), and hit efficiency (p = .014). Regarding academic stratification, the freshman to sophomore cohort (n = 15) significantly improved number of pitches (p = .018), innings pitched (p = .019), hits (p = .029), and strikeouts (p = .003). Whereas, the sophomore to junior cohort (n = 21) significantly improved losses (p = .042) and hit efficiency (p =.028). The findings from this study indicate that participation in a summer baseball league may have improved several critical pitching metrics with implications to enhance team performance.