I think that the "Yips" are caused by the fear of making a mistake. That is why you will see players with the "yips" make fabulous plays, but when they have time to think, errors are made. The case of the "yips" was part of the book "The Art of Fielding" in which shortstop Henry Skrimshander accidently hits his roomate in the head with a thrown ball. He subsequently gets the case of the "yips" with dire consequenses.