First of all there is the concept of mental rehearsal or visualisaton. Any form of mental visualisation is hypnotic, since it involves using the imagination to rehearse the future.
The second sports hypnosis principle, which follows on from mental rehearsal, is creating positive expectation. Expectation is a powerful force in human motivation and behavior.
The third sports hypnosis principle addresses the downside of the first two. It is, of course, quite possible to mentally rehearse failure and to build negative expectations!
Finally, sports hypnosis works on the principle of the mind-body connection.
Read full article here: Sports Hypnosis