The weigh-in for Billy Joe Saunders' fight with Willy Monroe Jr was interrupted on Friday when the Briton's young son attacked the title challenger on stage.
As the two fighters posed for photographs, Stevie Saunders moved between them before punching and kicking Monroe Jr below the belt.
The American had ruffled the young boy's hair but his friendliness was not reciprocated by the younger Saunders, who had to be dragged away by security after the attack.
"My son's been taught when a stranger puts their hands on them they don't know punch and run away: self defence," Saunders tweeted afterwards.
Both fighters had just weighed in at 11st 6lbs ahead of Saturday's showdown. They were flexing their muscles in front of the assembled media when Stevie attacked Monroe Jr, who seemed more shocked than hurt - despite being hit in a sensitive area.