Dog runs and play areas are wonderful, as long as you apply some safety rules. Some pups of small breeds need to be protected from themselves. They cannot be allowed to play with much larger animals no matter how much they want to romp. They are not aware of the risks they are taking. Some cities offer small-dog runs; seek these out (or create them) in your area.
While most adult dogs will give a young pup “carte blanche,” dogs just out of the young juvenile period may come down hard on the younger pups. Older pups nine to twelve months or so are often dishing out the roughest play in the run—not simply because they are young and exuberant, but also because they are protective of their new, tenuous ranking at the bottom of the group and always looking to move up a bit by putting some younger dog below them in line.
This normal, natural behavior needs to be watched. Allowing your pup to be played with roughly can look like great fun, but it increases the chances of injury (with your pup at greatest risk), and it teaches your pup to play this way when he reaches that age.
It is a better plan to have him play with calmer, older dogs, who likely won’t add to his energy level or play the canine version of “stuff his head in the toilet and flush.”
These adults will start setting clear boundaries when your pup reaches about five months old. They may growl at, pin, or stand over your pup, who may yelp, squeal, freeze in place, or urinate a bit. This is usually both normal and beneficial for dogs who will be doing a lot of group play in the future.
What is not normal is an adult dog who continues to go after the pup even when the pup has submitted (lowered his body, rolled over, lucked his tail). This needs to be stopped immediately but calmly.