Introduction: Elite football performance hinges on rapid tactical decision-making under physical and cognitive strain. While peripheral fatigue’s effects on motor output are well documented, the neurophysiological markers of mental fatigue and their impact on in-game decision making remain underexplored. Objective: To determine how EEG-derived central fatigue indices—frontal theta power and the theta/alpha ratio—relate to tactical decision accuracy and speed in elite football players. Methodology: Twenty male national-level footballers (age 22.4 ± 2.1 years; ≥ 5 years’ experience) completed the Yo-Yo Intermittent Recovery Test Level 1 while wearing an 8-channel dry-electrode frontal EEG headset. Frontal theta (4–7 Hz), alpha (8–12 Hz), and the theta/alpha ratio were extracted pre- and post-test. Decision-making was assessed via a validated 40-scenario video-based tactical test measuring accuracy (%) and reaction time (ms). Results: Post-fatigue, frontal theta increased by 45% and the theta/alpha ratio by 47% (both p < 0.001), while decision accuracy declined by 15% (p = 0.004) and reaction time slowed by 18% (p = 0.002). The theta/alpha ratio explained 52% of variance in decision accuracy (p < 0.001). Discussion: These findings confirm that wearable EEG markers sensitively capture central fatigue effects and directly predict tactical decision impairments, extending central fatigue theory to applied sport contexts. Conclusion: Frontal theta and the theta/alpha ratio are robust, portable biomarkers for monitoring cognitive fatigue in football, offering practical avenues for real-time performance management and optimized training or substitution strategies.