The chuck is stuck open - Dewalt DC920KA Heavy Duty Xrp 18V Cordless Drill/Driver

not much can be done as the chuck is not specifically designed to handle hammer drill operations (they crack the scroll thread adjuster inside )
best get a new chuck and if you do a lot of hammering get a proper hammer drill that has a push in operation not an ordinary electrical drill with a hammer capability

This is caused by tightening the chuck using the drills power, if you clamp the bit in a vice and using a pair of multi grips on the chuck in an anti clockwise direction gently bounce the grips and after a few tries it will undo, don't use too much pressure or try to unwind it in one move or myou will damage the chuck sleeve

Try holding the bit in a vice and gently tap the chuck off of the bit and see it it releases the pressure on the jaws.

If the chuck is stuck open and you cant "muscle" it closed something is probably jammed up in there and it needs to be replaced. Chucks take a good share of the abuse on power tools and most manufactuers consider them a "common wear item" like brake pads or Tires on your car. A chuck is fairly simple to replace if your drill stuck open and they are commonly replaced on the higher end "Industrial Grade" Power Tools like DeWalt and Milwaukee.
Looking at the Make and Model of your drill it would probably be easiest and most cost effective to just replace the entire drill. If you tried to replace the chuck and found a chuck that will fit your tool it may cost you anywhere from $25 - $40. For Around $40 you can purchase a new drill with a fresh battery.

It's just jammed in fully open position, take a set of channel lock pliers around the chuck and unstick it .

Hello. Wrap a towel around the chuck and use a pipe wrench or a pair of channel locks to put a little force on the chuck. J.

If you mean the chuck jaws seem stuck open, spray around them with some penetrating oil or spray like WD-40, RP-7 or similar and let sit for a couple hours... Then you can tap around the chuck body with a light hammer or spanner etc... just lightly tap... Then if the chuck has an arbor lock to prevcent it from spinning, be sure that is engaged then try to release the chuck jaws. Sounds like they are stuck open through tight friction or rusting on the inside edges (that you dont see). Be careful not to leave them in the fully open position when stored as this is exactly what can happen!

the chuck is broken inside if clicking. Ace and True Value stores sell chuck replacements

I'd put penetrating oil in it and tap the chuck with a plastic hammer. That should free it up.

Best rgrds, W/D

if chuck is wide open ,look down inside there should be an allen screw or bolt at the bottom of the chuck it should undo anti clocwise and the chuck comes off