[5] Horseman began his career with East End United and Wallaby Sports[6] before joining Wycombe Wanderers as a twenty-year-old in 1961.
In 1974/75 he was part of the Wycombe Wanderers team that reached the third round of the FA Cup for the first time, playing against first division Middlesbrough, then top of the table and managed by Jack Charlton.
The game at Loakes Park was covered by London Weekend Television's Big Match cameras and Boro scraped a 0–0 draw.
The side travelled up to Ayresome Park for the replay and a 30,128 crowd saw the semi-pros hold out until the last minute when David Armstrong slipped the ball past Wycombe goalkeeper John Maskell and into the bottom corner of the net.
In 1975/76 he played in both legs of the two-legged final tie in the Anglo-Italian Semi-Professional Trophy against A.C. Monza, which Wycombe won 2–1 on aggregate.