Where I used to keep my dogs, they didn't tell me about the group playtimes where they pretty much emptied the kennel out to clean up, and put the dogs in a fenced area and just let them do what they wanted to do. My dog Gus was roughed up by a very big Dobe, one of the biggest I have ever seen during the first session, and they brought them in before anything happened much. (I was told this by one of the many teen girls working there).
The second day, they did the same thing, and it got nasty. The Dobe bit Gus on his ears a couple of times and then on the back of the neck, and finally pushed him into Pit Bull mode and he retaliated. The Dobe came out the worst for it, but it was obvious when I came to pick him up the next day that he had been in some kind of fight. Even the bath and bubble gum scent couldn't hide the 6 or 7 punch holes in his ears, and the bruises on his neck were pretty bad.
They told me about the "play time" thing, and I wasn't happy about it. I really wasn't too concerned with Gus getting hurt, one dog, at least one dog under 125 pounds wasn't going to do a whole lot to him without paying the price and probably getting his butt kicked. That's what happened to the Dobe, he got chewed up pretty badly, and his owners raised hell about it when they came to get him while I was there complaining about it. I didn't take him back until the ownership had changed back to the original owners, who took out pairs of them at a time, and watched them closely.
My present dog King went to "doggy day care" and loved it. Sadly, his playmates didn't enjoy his roughness, and so they asked me not to bring him back, as there was a lot of tension that day, and they were afraid that King would hurt, unintentionally, the dogs in the smaller group, or get hurt by some of the bruisers in the larger one, as he was by far the smallest dog in it.He was the only dog in the 50-70 pound range that day. He took over both, and made enemies out of several of the dogs who were previosly bosses of the groups.