At the risk of having Morgan not agree with me (or anybody else), a defensive forward is somebody who is used to help lock the ball into the forward 50 to improve our chance of scoring if the first forward 50 entry didn't result in a goal.
Chris Mayne was very good at this as he would run like a maniac, apply pressure and sometimes get the ball turned over. Unfortunately, he often missed the goal, thereby kind of ruining the whole idea.
But thats the idea of a defensive forward.
that....and what Shane said.
(ps. dont listen to polly....and don't tell him I said that)