William Joseph Addison (born 20 August 1992) is an English-born Irish rugby union player who plays as a utility back for Premiership Rugby club Sale Sharks, and has represented Ireland internationally.

[8] His contract with Sale contained an option to leave if an Irish team approached him,[9] and he signed for Ulster ahead of the 2018–19 season in pursuit of his ambitions to play international rugby.

[12] He sustained a back injury in January 2019 that required surgery[10] and kept him out for fifteen months.

He returned to action in April 2021, before his season was ended by a red card for a dangerous tackle against Munster in May.

[13] He started the 2021–22 season strongly, playing four games and scoring a try,[14] before sustaining a fracture of the lower leg in October which again meant undergoing surgery.