Knobel, a ruckman originally from the Gold Coast, was recruited to the AFL in his home state with the Brisbane Lions onto their rookie list.
[citation needed] After a disappointing 2001 season, and with the Lions having an abundance of ruck stocks (Keating, Charman, McDonald, McLaren among others), they traded him to St Kilda.
Despite his crash and bash ruckwork and tally of 460 hitouts for the year, he was criticised for his lack of around the ground work, averaging just 6 disposals in 2004.
[citation needed] This led to him being delisted by St Kilda, before being selected in the 2005 pre-season draft by the Richmond Football Club.
Due to ongoing injury concerns Knobel was unable to play a senior game in 2007 and announced his retirement from AFL football on 28 August 2007.