This randomized, double-blind, placebo-controlled, parallel-group trial will evaluate the effects of 14 days of taurine-caffeine supplementation with or without phosphatidylserine on neurocognitive fatigue resistance, visual search efficiency, and football-specific tactical decision-making in professional male football players. Sixty-two male outfield football players from two professional clubs will be randomized to placebo, taurine plus caffeine, or taurine plus caffeine plus phosphatidylserine. Laboratory and field-based outcomes will be assessed at baseline and after the supplementation period.

This study is designed to determine whether adding phosphatidylserine to a taurine-caffeine supplementation strategy supports attentional control, efficient visual search, and accurate tactical decision-making under acute neurocognitive load in professional male football players.

Participants will complete familiarization, baseline laboratory testing, baseline field testing, 14 days of supplementation, post-intervention laboratory testing, and post-intervention field testing. The laboratory protocol will include a high-load Stroop/Flanker task followed by a football-specific video decision-making task with screen-based eye-tracking. The video task will include offensive and transitional football situations requiring players to select the most appropriate tactical option under time pressure. Some clips will require inhibition of an immediately attractive but suboptimal forward action.

The primary outcome will be the change in tactical inhibitory decision accuracy under neurocognitive load from baseline to post-intervention. Secondary outcomes will include overall decision accuracy, decision time, impulsive tactical errors, mental fatigue, Stroop/Flanker reaction-time variability, time to first fixation on the optimal option, dwell time on the optimal option, situational awareness accuracy, and field-based reactive passing decision performance. Field-based transfer will be assessed using a Reactive Passing Decision Test, the Loughborough Soccer Passing Test, and standardized small-sided games.

Inclusion Criteria:

• Male professional outfield football players aged 18 to 37 years.
• First-team players or selected U19 players aged 18 years or older who are regularly integrated into first-team training.
• Regular participation in club training.
• At least 5 years of systematic football training experience.
• Free from injury or illness limiting full participation in training and testing.
• Normal or corrected-to-normal vision.
• Ability to complete the laboratory and field-based testing procedures.
• Written informed consent provided before participation.

Exclusion Criteria:

• Goalkeepers.
• Current injury or illness limiting full participation in testing.
• Neurological disease.
• Recent concussion or head trauma.
• Uncorrected visual impairment.
• Use of phosphatidylserine, nootropic agents, or strong stimulants during the previous 4 weeks.
• Non-standard caffeine intake on testing days.
• Failure to comply with pre-test standardization procedures.
• Failed eye-tracker calibration.
• Loss of more than 30% of gaze data during the football-specific decision-making task.
• Withdrawal of consent.

No individual participant data will be shared because the study includes a small sample of professional football players from a limited number of clubs, which may increase the risk of indirect participant identification. Only aggregated and anonymized study results will be reported.

Participants will be randomized in a 1:1:1 ratio to one of three parallel groups: placebo, taurine plus caffeine, or taurine plus caffeine plus phosphatidylserine. The intervention will last 14 days, and outcomes will be assessed at baseline and after the supplementation period.