The weigh-in for Billy Joe Saunders and Willie Monroe Jr's WBO middleweight title fight was disrupted when the English boxer's son attacked his opponent.

Saunders, who won his title against Limerick's Andy Lee in December 2015, is set to make this second defence in London against American Willie Monroe Jr tomorrow.

As Monroe Jr weighed in this afternoon, Saunders' son put his foot on the scales. Monroe tousled his hair playfully and the youngster reacted by punching his father's opponent in the groin and aiming a kick at him.

Defending his son's antics, and suggesting Monroe's head pat was more than that, Saunders Snr tweeted: "My sons been taught when A stranger puts their hands on them they don't know punch and run away self defence."