Originally from the University Blues, Ainsworth was used as a back pocket by Geelong over the course of his eight season career. He was a member of Geelong's losing 1967 VFL Grand Final side in his first year at the club. After missing all but one game of the 1971 season as he was traveling in Europe, Ainsworth went on to become club captain in 1973. He lost the captaincy role the following season and retired, aged only 28, at the end of the year in order to concentrate on his legal career. During his career Ainsworth had polled a total of five Brownlow Medal votes. In 1976 he was made a life member of the Geelong Football Club. Ainsworth died on 2 February 2011.