<p>The current study aimed to examine and compare the impact of a high-intensity interval training intervention during the off-season period to a non-exercising control in sub-elite (club level/Tier 2: Trained/Developmental) male Gaelic football players. Twenty-two players from one sub-elite team underwent anthropometric (body mass, sum of seven skinfolds) and performance (right-hand grip strength, countermovement jump (CMJ), static jump (SJ), sprint tests, Yo-Yo Intermittent Recovery Test Level 2 (Yo-YoIRT2), repeated sprint ability (RSA) and 1-km time trial (TT)) assessments at two time points (pre- and post-intervention). Players were assigned to a control (detraining) group or an intervention (running) group. There was a significant interaction for the multivariate main effect between time and group (F _{(12, 8)} = 6.849; <i>p</i> = 0.005; _pƞ² = 0.911). A significant interaction was observed for Yo-YoIRT2 (F _{(1, 19)} = 15.761; <i>p</i> ≤ 0.001; _pƞ² = 0.453), RSA average (F _{(1, 19)} = 39.199; <i>p</i> ≤ 0.001; _pƞ² = 0.674) and TT (F _{(1, 19)} = 29.356; <i>p</i> ≤ 0.001; _pƞ² = 0.607), with a marginal interaction observed for both 10-m sprint time (F _{(1, 19)} = 6.863; <i>p</i> = 0.017; _pƞ² = 0.265) and RSA decrement (F _{(1, 19)} = 6.54; <i>p</i> = 0.019; _pƞ² = 0.256). There was no significant interaction for body mass, the sum of seven skinfolds, right-hand grip strength, CMJ, SJ, 5-m sprint time and 20-m sprint time (<i>p</i> &gt; 0.05). The data obtained highlight the negative impact detraining may have on physical performance within Gaelic football and suggest that the inclusion of a moderate, off-season high-intensity interval training can limit many of the physiological declines. The findings may aid coaches in developing training regimes to better manage the off-season period while preparing players for the upcoming pre-season.</p>