How to safely remove pump off presta valve?
I used to skin my knuckles every time I took the chuck off the valve.  Then I figured it out (pain is a learning curve accelerator).

Position the wheel so the presta valve is closest to you and pointed away from you.  Use your thumbs on either side of the wheel to push the chuck straight off (toward the hub of the wheel).

This prevents the presta stem from being bent/broken and limits how far you hands can move when the chuck pops off.  No more bashed knuckles.