When you score a TD and the word touchdown first appears press the following button combinations.

L+B: spike ball,Points to crowd and hits chest
L+Y: bows to crowd
L+X: Spikes ball and shrugs shoulders
L+A: Heisman Trophy pose
R+B: dunk on goal post
R+X: puch ball towards crowd
R+Y:Kick ball into crowd
R+A: throws ball into crowd

Note: You can get a 15 yard penalty for unsportsmanlike conduct.