This observational study aims to investigate the association between brain type, determined by the second-to-fourth digit (2D:4D) ratio, playing position, and mental toughness among amateur soccer players. A total of 270 licensed amateur soccer players participated in the study. Mental toughness was assessed using the Sports Mental Toughness Questionnaire (SMTQ), while brain type was determined by measuring the 2D:4D digit ratio. The study examines whether mental toughness differs according to brain type and playing position, providing insight into the neuropsychological characteristics of soccer players and their potential relationship with psychological performance.

Inclusion Criteria:

• Licensed amateur soccer player.
• Aged between 16 and 40 years.
• Currently participating in regular soccer training and competitions.
• Able to understand and complete the Sports Mental Toughness Questionnaire (SMTQ).
• Provided written informed consent prior to participation.

Exclusion Criteria:

• Professional soccer players.
• History of neurological or psychiatric disorders that could affect psychological assessment.
• Upper extremity deformity or injury preventing accurate 2D:4D measurement.
• Incomplete questionnaire or missing study data.
• Declined or withdrew informed consent.

Licensed amateur soccer players recruited from amateur soccer clubs in Denizli, Türkiye. Participants represented different playing positions, including goalkeepers, defenders, midfielders, and strikers.