What do you mean by "playing"?

"Playing around" is Tianjin's name for local ruffians, which is different from the underworld.

First: they don't bargain for a living. They fight just for fun.

Second, they don't have the three conditions for the formation of "underworld" (a certain economic foundation, a strong local umbrella and complicated social relations). They are generally "skirmishers" and cannot form complex social relations.