The 'As Long As You Love Me' singer - who is desperately trying to win back his on/off girlfriend of two years Selena Gomez by showing her how mature he is - has been accused of hitting a female security guard at a concert venue he was performing at in Ottawa, Canada in November, with a projectile from a child friendly nerf gun.
A source told gossip website TMZ.com that the 18-year-old Canadian popstar was play fighting with nerf guns with his three-year-old brother Jaxon and four-year-old sister Jazmyn, when one of their soft pieces of ammunition hit the woman.
The woman allegedly became hysterical and told Justin's team that she was a security guard at the venue and was extremely annoyed.
She then filed a police report accusing Justin or someone who was adjacent to the singer of assaulting her.
Police are said to be investigating the incident and have interviewed several people at the venue.
Justin was forced to deny reports he mocked a female fan in a gym earlier this week after he declined to take a photo with her.
But friends close to the singer have insisted he is trying to be on his best behaviour at the moment to prove to Selena, 20, that he has grown up.
However, Selena has reportedly moved on after telling friends that Justin was too needy for her.
A source said: "Justin is super needy and can be a big baby around Selena. It's hard for him to make real friends because he likes the temporary attention of strangers, but didn't see how it hurt Selena.
"Selena didn't feel Justin was respectful of their relationship. She was constantly catching him in positions with other girls that would make her uncomfortable. She would get super jealous."
The couple broke up shortly after holidaying in Mexico where they had planned to ring in the New Year together but got into a huge argument on December 30 after she allegedly found text messages from other girls on his phone.
- BANG! Showbiz