Pavise Crossbowmen.
Nuff' said.
I thought Pavise Crossbowmen only brought shields to stick them into the ground, like rudimentary siege shields. Not carry them on the back while firing/reloading.
And for the argument's sake, I don't see how it would be possible for them to jump around with a heavy polearm and swinging it simultaneously.
They would have turned around whilst reloading their crossbows, which would have taken some time. They then turn back around, shoot, repeat.