Knapman played fullback in Oldham's 2–13 defeat by Wigan in the Championship Final during the 1921–22 season at The Cliff, Broughton on Saturday 6 May 1922.

Knapman played fullback, and scored a penalty goal in Oldham's 4–21 defeat by Wigan in the 1924 Challenge Cup Final during the 1923–24 season at Athletic Grounds, Rochdale on Saturday 12 April 1924.

About Knapman's time, there was Oldham's 5–7 defeat by Warrington in the 1921 Lancashire Cup Final during the 1921–22 season at The Cliff, Broughton, Salford on Saturday 3 December 1921, and played fullback in the 10–0 victory over St Helens Recs in the 1924 Lancashire Cup Final during the 1924–25 season at The Willows, Salford on Saturday 22 November 1924.

One of the finest defensive players in the League is Ernest Knapman, who joined Oldham in January 1921.

He played as schoolboy for Upton School, Torquay, and in 1920 was full back for his town fifteen.