How to fight on L.A. Noire? (Xbox 360)?

On some cases in L.A. Noire on Xbox 360 the suspects who you are questioning fight with you and start to punch you.

I press all the buttons on the controller but the officer does not seem to fight back!

I keep failing cases because of Officer Down because i do not know how to fight.

Please can someone tell me how to fight on L.A. Noire on Xbox 360?How to fight on L.A. Noire? (Xbox 360)?
on ps3, you have to hold down R2 or L2, then push x or circle.