Too much wiggling when trying to remove the pump head (chuck).

Two things here. One is try not to push teh pump head down too much. The other is once you have flipped the lever back on the pump head to release the valve then turn your wiggling motion to a gentle twisting. Be careful though, if the valve looks like it's twisting as well then stop.

Other hint is hold the wheel so that the palm is on the tire and you have a finger either side of the valve. Hold teh pump head with the other hand and pull striaght. If possible use your body weight.