Background: Rugby is a collision-based team sport requiring repeated high-intensity sprinting, technical execution, and physical contact under fatigue. Although caffeine is used as an ergogenic supplement, evidence from mixed team-sport populations may not be applicable to rugby. This systematic review evaluated the effects of acute caffeine supplementation on physical and sport-specific performance, perceptual responses, and physiological markers in rugby players. Methods: PubMed, Web of Science, Cochrane Library, Scopus, and Embase were searched from inception to May 1, 2026. Randomized placebo-controlled studies examining acute caffeine supplementation in rugby players were included in the quantitative synthesis, whereas observational studies related to sleep and recovery were narratively summarized. Standardized mean differences were calculated as Hedges` g with 95% confidence intervals. Three-level random-effects models accounted for dependent effect sizes. Methodological quality and risk of bias in randomized trials were assessed using the PEDro scale and RoB 2, respectively. Observational studies were assessed using the JBI checklist, and certainty of evidence was evaluated using GRADE. Results: Fifteen studies were included, and 13 randomized placebo-controlled trials contributed data to the meta-analysis. Acute caffeine supplementation was associated with small improvements in sprint performance (k=11, Hedges` g=-0.41, 95% CI: -0.73 to -0.08, p=0.02) and lower rating of perceived exertion (RPE) measured during or immediately after rugby-specific or resistance-exercise protocols (k=9, Hedges` g=-0.40, 95% CI: -0.73 to -0.06, p=0.02). A large positive effect was observed for passing accuracy (k=9, Hedges` g =1.65, 95% CI: 0.69 to 2.61, p=0.004), but this finding showed high heterogeneity and potential small-study effects. No significant effects were found for jumping performance, strength performance, metabolic markers, or hormonal markers. Subgroup analyses did not identify moderating effects of rugby code, dose, form of administration, or competitive level. Observational evidence suggested possible sleep and recovery concerns following caffeine exposure. Conclusion: In rugby players, acute caffeine may improve sprint performance and passing accuracy while reducing RPE measured during or immediately after rugby-specific or resistance-exercise protocols. However, certainty of evidence ranged from low to very low, and findings should be interpreted cautiously.
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