You might need to remove the end cap on your softball bat for a variety of reasons. Fiber can loosen within a bat and rattle around, which is distracting. Cap removal is sometimes needed to determine how deep a surface crack is. Another reason to remove the cap is to shave the bat, a process that thins the bat's inner walls to increase how far a ball will go when hit. Bat shaving is generally performed for home run derbies, tournaments and practice purposes, and is illegal in most league play.
Boil about a quart of water and use a cooking thermometer to test the temperature. Water temperature should be between 50 and 80 degrees Fahrenheit to cause the bat's fibers to expand. Pour the water into a bucket and place the bat in the water, bat cap side down, for about 1 minute. You do not have to submerge the entire bat, just the end with the cap.
Place the barrel of the bat in a standard industrial vice and turn the crank as needed until the bat is firmly locked into the vice. You should be able to see the seal between the bat cap and the rest of the bat. Avoid over-tightening the vice, as this can squeeze and deform the bat.
Place a thin pry bar in the sealed area and hit the other end of the bar with your hammer. The applied heat should make the cap come off with one or two hits. Apply the pry bar to the bat on an angle rather than straight through to avoid injuring the bat cap.