According to Jan Graydon, Ph.D., Head of the School of Sport, Exercise & Health Science at University College Chichester, an athlete's sport performance improves with increases in arousal until a peak is reached, after which continued arousal leads to a deterioration in their performance. She also states that arousal can be beneficial, but only if an athlete is already accomplished at the task they're performing. The causes of anxiety in sports are manifold, but some sources of anxiety are more universal than others.
Performance Anxiety
According to the Social Anxiety Institute, social anxiety disorder, also known as performance anxiety, is a persistent fear of performance situations--such as an athletic event--in which you're exposed to unfamiliar people or to possible judgement by others. Performance anxiety can be felt by everyone, but athletes and performers are particularly susceptible to its crippling effects because of the very public nature of their efforts. With sports performance anxiety, athletes fear that they will perform their activity or sport in a way that will cause them to feel embarrassment or humiliation. In some instances, performance anxiety can lead to panic attacks and a complete inability to perform a task that the athlete, in a non-competitive setting, have flawlessly performed countless times. Most athletes that suffer from performance anxiety understand that their fear is unfounded, but this realization may do little to help them cope with this stress. Athletes can with a sports psychologist to overcome any fears and optimize their performance.
Fear of Failure and Rejection
For many people, according to Dr. John Douillard, a Boulder, Colorado-based chiropractor and author of the book "Body, Mind, and Sport," the first major failure in life often is a sports-related failure, perhaps a humiliating incident in a physical education class or an embarrassing performance in an intramural sport. The fear of failure and rejection can start at a young age and continue into adulthood if not dealt with properly. SelfGrowth.com states that playing tentatively or playing to avoid mistakes can hinder the ability to succeed, can have detrimental effects on a performance and can be a source of self-perpetuating failure, which may cause players to drop out of their sport. Athletes should consider reframing their reasons for sport participation. Instead of focusing on a goal-oriented approach that measures success by a specific outcome, athletes can try to cultivate a process-oriented approach that focuses on the aspects of the sport that they find enjoyable.
Injuries
Athletic injuries can cause sports-related anxiety, as injuries may directly affect an athlete's ability to perform an activity they enjoy or an activity through which they derive their livelihood. According to SportsInjuryBulletin.com, while sports injuries may cause players to experience stress, sports-related stress or anxiety may predispose them to injuries. In sport situations that are considered stressful, athletes may experience attentional narrowing and excessive tension in the muscles, both of which are believed to elevate the likelihood of sustaining an injury. Attentional narrowing is particularly problematic, especially if someone is playing a contact sport, because this may cause them to miss important peripheral cues. Learning to cope with stressful athletic situations can help people avoid attentional disruption and excessive muscular tension, which in turn may reduce their likelihood of experiencing an injury during the sporting event.


