Roughousing, sometimes mock-wrestling, usually between two boys of similar age. "Horseplay" at first glance looks like actual fighting or wrestling until the more playful "fooling around" element become visible, but horseplay sometimes can deteriorate into real fighting.
A Midwestern urban regionalism means the same but includes a "get your back" connotation: grabass. No one considers that homoerotic.
"I told you, boys, no horseplay standing in line. You're not getting into the theater if you don't stopfooling around like that."