As an amateur Knoetze fought future professional world champion fellow South African Gerrie Coetzee six times, each winning three bouts.[1]

Knoetze turned professional in 1976, and started his career with six consecutive KO wins. In his seventh fight he was disqualified against Reinaldo Raul Gorosito, and in his eighth bout he lost a ten rounds points decision to Coetzee.

From late 1976 to 1979 he went on a 11-fight winning streak, which included avenging his loss to Gorosito via a ten rounds decision (this was the only bout in the streak that went to the distance) and knocking out US Olympian Duane Bobick and former Muhammad Ali opponent Richard Dunn.

In 1979 he was rated as the number three heavyweight in the world, and fought an elimination bout for the vacant WBA heavyweight belt, but he lost to another US Olympian, John Tate, via an eighth round knockout. In the other elimination bout Coetzee defeated Leon Spinks and then went on to lose to Tate for the WBA title himself.

Knoetze never fought for a major title again. He fought seven more bouts, winning four and losing three, before retiring in 1981 after a second round knockout loss to Robbie Williams

Between 1979 and 1991 Knoetze acted in four movies, his best known role being primary antagonist Rosco Dunn, a former corrupt professional boxer turned to a military sergeant, in the 1982 Bud Spencer hit Bomber.