The poses should prolly be a bit more dramatized.  They're too similar for there to be any sort of oomph to the switch.  Maybe raise the arms/hands into a more boxing-like position? 

Otherwise, the yellow leg kind of swaps sizes a few times, and the knee doesn't align well with the blue one.  It also shifts to the side without any sort of turn.  Slightly turning the yellow foot to make it face the screen would improve that.

What kind of battle would he be taking part on? Is he a hand-to-hand fighter, an armored knight, a soldier?

Right now it doesn't really look like a battle stance, feels more as if he was about to jump. Some kind of guard pose with raised arms as mentioned would convey the feeling of battle better.

You're making the head bob by stretching the abdomen. Maybe the characters abdomen stretches but the reason the head usually bobs is actually the legs bending and rotating which moves the pelvis up and down, so if the pelvis doesn't move up and down you know your legs are actually growing and shrinking. I see the pelvis blob moving but it doesn't appear to be attached to the movement of the legs in any way.

Ditto on the arm going straight at the back.

it feels like they're pushing their arm back when it straightens out like that, keep working with it.
Also, they alternate with the legs. So when blueleg is going forward, so would red arm, and when (orange? yellow? colorblind, can't tell) leg goes forward, that's when green arm would go forward.

you can see examples of this around on the street when people are walking normally, it's a thing our body does to counterbalance our gait.