A ball faucet has a metal or plastic ball with grooves that control flow. Small springs press rubber seats against the ball. Replacing the seats and springs usually will stop a leak. However, the ball may also need to be replaced.
Tightening the adjusting ring with pliers or a special tool may stop a leak. If water flow is slow or erratic, remove the seats and springs and flush out any debris.
An hour or two for most repairs
Screwdrivers, adjustable wrench, groove-joint pliers
Shutting off water, dismantling a faucet, installing small parts
Shut off the water, close the tub stopper, and place a rag in the tub to catch any parts
O-rings, seats, other rubber parts, silicone grease, cylinder if needed