I read a comment here not long ago that there was a guy who had a stutter +40 years and after an accident his stutter was gone. His theory was because he forgot he had a stutter. There is a hyphothesis called "Anticipatory Struggle Hyphotesis". The theory explains that is it when we anticipate that we will stutter that we ourself create the stuttering. This can occur below level of consciousness. It seems that when you focus your attention on words you are creating the struggle. When you are playing sports you momentatily "forget" that you have a stutter and the stutter dont have the cue to build up. The problem is that is very hard to try to not think about something. When you try to do that the though only gets more recurrent.