A mental block is a psychological barrier that stops an athlete from performing a skill they are otherwise physically capable of executing. The classic example is in gymnastics or diving, where an athlete suddenly cannot perform a skill they've done countless times before — but mental blocks appear across many sports.
Mental blocks are typically driven by fear and anxiety — fear of injury, fear of failure, or a loss of trust in one's own body (such as losing air awareness in aerial skills). The conscious mind effectively overrides an automatic movement, freezing it. They can be frightening and frustrating, and they are not a sign of weakness or lack of commitment.
Overcoming a mental block usually involves a patient, layered approach: regulating arousal and fear, rebuilding confidence in the skill gradually, using visualization to mentally rehearse successful execution, and often breaking the skill down and rebuilding it in steps. Because blocks can be deeply rooted, working with experienced coaches — and qualified professionals where needed — is often valuable. Related to the concept of the yips.