Turnbull made his debut for West Coast in round seven of the 1991 season, against Hawthorn at Princes Park, as the youngest member of the team, gathering nine disposals and effecting four hit-outs partnered with Dean Irving.
[4] He played four further games in the 1991 season, being kept out of the side by older, more experienced key-position players such as Michael Brennan, Ashley McIntosh, Glen Jakovich, Dean Irving and Stevan Jackson.
[6] Turnbull managed six games in 1992, including five of the Eagles' first seven, but was again kept out of the side by first-choice ruckman Paul Harding.
He did not play for the Eagles in 1993, mainly due to the form of Irving and Harding, but managed to win a second F. D. Book Medal.
[5][8][9] He was named as the ruckman in the Eagles' Team of the Decade, announced in 1996 to coincide with the AFL's centenary celebrations.
Turnbull did not play for the Eagles in the 1999 season, with Gardiner and Jason Ball the first-choice ruck combination.
He played 17 games for East Perth in the WAFL, and was considered one of the favourites for the Sandover Medal, eventually losing to Gus Seebeck by one vote.
He played 17 games for East Perth in 2001, including in the 2001 premiership team, winning the Simpson Medal as the best on ground in the Grand Final.