What did he do?

0125_justin_bieber_nerf_fight_Article_getty_tmz

He was in Ottawa, Canada in November when a female employee of the venue where he was performing filed a police report, claiming Bieber assaulted her.

The woman told Canadian cops she was hit by something.

It turns out it was a kid-safe projectile from a Nerf gun.  Sources familiar with the situation tell TMZ ... Justin was Nerf fighting with his 3-year-old brother and 4-year-old sister and apparently one of the darts hit the woman. She filed a police report and the cops are actually taking it seriously!

(TMZ)