Here I've mostly just tried to sort out the stampy feet a little more by bringing the knee forward on the passing position so there's more change between keys. I think it's looking better, although there's a bit of popping with the back leg and I think the up and down movement might be a little bit bumpy? He does seem to rise up quite high on the 'up' pose so maybe dropping the height slightly would rectify that, although that would make the knee bend, which would mean I need to bring the leg further back to straighten it, which may then cause problems with the contact pose - the contact pose's back leg is already stretched almost as far as it will go without popping out of place so I'm not sure what else I can do.
The popping, I think, may be caused by the spacing of the leg between the passing and contact poses. I could try bringing the leg of the passing and up positions forward so that there's more change between them.
Really, though, I think that the problem is the contact pose? Maybe he's up too high. If I lower him slightly I might be able to extend the back leg a little more. I'm wary of lengthening the stride too much... don't want it too exagerrated.