from urbandictionary.com Flagging (v) The act of pulling another person's pants down. My brother got in-school suspension after flagging a girl in gym.
seem slike it was more popular in the 80s and 90s...don't know if kids these days know about flagging. Probably because most of them already wear their pants down to their knees anyways.
I've never heard that called flagging. We would say you got pantsed. I got flagged at track once standing at the bottom of the bleachers in front of the whole team.
people would try that shit all the time in gym everyone was always looking over their shoulder all paranoid.