My Bobbie has an attitude, she knows how to play fetch she just doesn't see the sense in bringing the ball back to us if all we are going to do is throw it again. As you call her to bring it back she looks at you cocks her head, grins, then turns her back on you and does her own thing. Chester on the other hand could play fetch all day and never tire of it. Bobbie is trying her hardest to break him of this habit by stealing his toys before he acn get to them. Dogs are characters, maybe your dog just has an attitude like Bobbie.