What makes the player animate its legs?

Ive got a new player model into the game. Just copied most of the info from the existing player.cs etc.

Anyhow, he has idle, run and back anims at the moment, but sometimes the run isnt being played.

Ive messed with the max velocities and stuff, but cant get a consistant use of the run anim.

What are the rules about when the run anim is played compared to the idle?

i know there is a movement in the max model, we already have that covered. Like i said, sometimes he animates his legs as expected, but other times he doesnt.

Any idea's for what to tweak?

Phil.