According to Gossip Center, the Boyfriend singer and Gomez were leaving a cinema after watching a film together in Los Angeles when they were surrounded by snappers.
The website reports that JB saw red when one of the photographers got too close, resulting in the 18-year old losing his hat and a shoe, which lead to the fight.
Selena apparently managed to calm Justin down and he then escaped the scene by running to a waiting van. Gomez is then said to have fled, quickly following her beau to the vehicle.
A source told Gossip Center: "Los Angeles County paramedics arrived at the Calabasas Commons with the Fire Department and Police arriving moments later following Justin's altercation with a paparazzo. Justin's bodyguard [also] arrived while the photographer received medical attention for an apparent strike to the face."
Gomez later addressed the episode on Facebook, writing: "THANKS YOU SO MUCH to my fans for always protecting me and being there for me. I can't thank you guys enough. I'm sorry I had to rush out. Love you guys. (sic)."
Last week, Biebs confessed that he almost quit music due to the pressures of fame, telling The Hollywood Reporter: "There were so many times when I just wanted to say, 'Enough is enough, I don't want to do this any more'."