Rough play

Tucker and I went over to the dog park the other day.  At first there was one other dog there and he and Tucker started playing nicely together.  A little while later another dog and owner came in.  The dog appeared to be a puppy but was of course still three times as big as Tuck; he looked a lot like a black lab, but possibly had something else mixed with him (pitbull??).  Things started off fine.  First, the two larger (than Tucker at least) dogs were playing with each other.  Then the black lab began chasing Tucker, which he absolutely loves.  He tends to try to provoke bigger dogs to chase him around, and it's usually pretty darn cute.  Anyway, the innocent chasing turned a different direction as the lab started "pinning" Tucker down, and then he started "biting" (mouthing? play-biting?) at him.  The owner was standing near me and said to let her know if her dog was being too rough, and that she was still trying to learn about dog play behavior.  I completely agree though; I don't want to be the crazy, overprotective "mom" running after my dog when he's simply and innocently playing and having fun with another pooch.  I soon thereafter realized I was not comfortable with what was going on, even though Tucker didn't appear frightened or make any nervous or "I'm in pain" sounds.  I picked him up and walked over to grab his leash, but he wriggled and jumped out of my arms.  The other dog pinned him down on his back again and I was gently yet forcefully trying to push him off of Tucker.  I grabbed Tuck again and got his leash on and off we went.  Tucker was totally fine after this incident (well, he had dog slobber all over him), but it made me decide that it's okay to break up doggie play if I feel uncomfortable with it.  Tucker is a smaller dog and often he doesn't realize it and neither do larger dogs.