This study will investigate static and dynamic postural control characteristics in male amateur football players with chronic ankle instability (CAI) compared with football players without ankle instability. Participants will undergo standardized biomechanical assessments using a force-platform-based postural analysis system to quantify postural sway under eyes-open and eyes-closed conditions and to evaluate direction-specific limits of stability performance.

In addition to conventional between-group comparisons, objective balance and stabilization variables will be used to develop supervised machine-learning classification models. These models will examine whether athletes demonstrating CAI-like functional patterns can be identified based solely on biomechanical performance data, independent of self-reported instability questionnaires.

The results are expected to enhance understanding of neuromuscular control deficits associated with chronic ankle instability and to support the development of objective, performance-based assessment approaches for football players.

The aim of this study is to determine the differences in static and dynamic postural control between amateur football players with and without chronic ankle instability and to evaluate whether multidimensional biomechanical balance parameters can be used to objectively characterize CAI-related functional profiles using machine-learning-based analysis.

Inclusion Criteria:

• Male amateur football players with at least 2 years of competitive participation and ≥5 years of regular sports activity
• Weekly football training volume of at least 3 hours
• For the CAI group: history of ≥1 significant lateral ankle sprain occurring ≥12 months before testing that caused pain, swelling, and temporary interruption of sports participation
• Presence of ≥2 episodes of giving-way or perceived ankle instability within the previous 6 months
• CAIT score ≤24 for classification as chronic ankle instability
• For the control group: no history of ankle sprain or perceived ankle instability and CAIT score ≥25
• Participants free from ankle pain and acute inflammation at the time of assessment

Exclusion Criteria:

• History of lower-extremity fracture or surgical intervention
• Musculoskeletal injury of the knee, hip, or spine within the last 3 months
• Diagnosed vestibular disorder or systemic balance impairment unrelated to the ankle
• Active ankle pain or acute inflammatory symptoms at the time of testing
• Any cardiovascular or systemic disease limiting safe participation in testing

Male amateur football players competing in a regional league, including athletes with and without chronic ankle instability.