I need some opinions on dog play

[BostonBully]

Ok my dog is in an obedience class and for the first fifteen minutes all the dogs get to play. All the dogs are under a year old. My dog is 5 1/2 months old. My dog from what I can tell shows pretty dominate behavior. He doesn't show aggression and never barks at the other dogs he just wants to play. It is strange because very small dogs he doesnt bother but most of the other dogs he runs after nipping and licking their legs or whatever he can reach. He doesn't bite them. He also wrestles with them and their isn't a dog he can't slam to the ground but when he gets them down he just stands over them and does not let them get up. No matter how tired he is he just doesn't slow down which tends to make play time get worse because the other dogs are tired. Once play time is over he is great at obedience and doesn't even pay any attention to the other dogs.

He really only plays well with two labs that are their. I'm not sure what it is about them but if he knocks them to the ground he will jump on them but he will also roll onto his back and let them jump on him. He has a blast playing so I'm not sure what to do. Any opinions?

[BostonBully]

He isn't from game blood. He is from UKC blood but I get what you are saying. He just plays alot ruffer and is so much stronger then any of the other dogs. They get pissed off when he doesn't let up. He never growls or barks but when they start too he gets angry and really wont let them get up off the ground.