Dog Park

Just got back from the dog park. Wilson had a great time. He loves to be chased by other dogs and will get a train of about five dogs chasing him around. For his size he is quite fast, but even still he does get caught and almost always gets hurt. Whether he just gets stepped on or gets a nip on his back from a riled up dog, he immediately stops and comes to me. He won't even look at another dog after that, just sit between my legs as if he needs protecting. Is it bad for my dog to be this sensitive? I assume he just got knocked down a few pegs on the dog totem pole and instead of climbing back up he just wants to leave and retry again another day. I'll have to read into that a little more.