I have been stringing a high school kids racket for him for awhile now. He usually plays with some cheaper Wilson string. I think it is either Sensation or Stamina or something like that. He didn't have any Wilson string the other day, so I strung his racket with Gamma Stinger 16/17. It is a hybrid, that has Polyester for the mains, and multifilament for the crosses. I personally love the way the Gamma Stinger plays. However, I was told by his coach that he went to play with the new string at a tournament, and played horribly!! He double faulted all over the place. All of his serves kept going 2 or 3 feet long. The HS kid claimed it was the string. He said he was swinging the way he always does, but the ball would NOT stay in, especially on the serves. He plays with a Technifibre 305 racket or something like that. He is NOT a power player. He is more of a loopy, medium racket speed type player. I checked my stringing machine to make sure nothing was out of adjustment. Do you think his problem was the strings??? Or do you think he was playing bad and blamed it on the strings??? I am new to Poly, but personally love the way it plays. Any help is greatly appreciated.