A brake caliper that will not retract - it clamps the pad on but never fully releases - is a common and damaging fault. The wheel drags, heats up, wears its pad fast, and can pull the car. Here is why a caliper sticks applied and how it gets fixed.
Seized caliper piston
The most direct cause is a seized caliper piston. Corrosion or a torn dust boot lets rust and grime build up, so the piston pushes out to brake but cannot slide back. The result is a pad held against the rotor - constant drag, a hot wheel, and rapid inner-pad wear you can read in the wear pattern.
Frozen slide pins
On a floating caliper, seized slide pins stop the caliper body from floating back, so it cannot release evenly. This is a cheaper, more common cause than a seized piston and shows up as uneven pad wear side to side. Cleaning and re-greasing or replacing the pins often fixes it.
A collapsed brake hose
Sometimes the caliper is fine but a deteriorated brake hose acts like a one-way valve, trapping pressure so the caliper cannot release - see when to replace a brake hose. This mimics a seized caliper and causes the same drag and pull; see why brakes pull.
The fix
Diagnosis works backward: check the slide pins first (cheap), then the hose, then the piston. A seized piston means rebuilding or replacing the caliper - see rebuild vs replace. Whatever the cause, fix it before fitting new pads, then install quality pads and fresh hardware.