There are really only three ways that
professional wrestlers bleed during
a match.
1) Blading. This is the most common way. A wrestler
will conceal a razor blade in their tights or in their wrist tape.
When he's supposed to bleed, he'll get out of the camera's view and run
the blade across his forehead. If done correctly, it will cause
a lot of blood to cover the wrestler's face in a short amount of time.
Wrestlers will NEVER, EVER cut themselves anywhere else on the body, as
the forehead is just about the ONLY safe place to do it.
2) Hardway. This is a legitimate cut or injury incurred
during a match. Broken noses, boxed ears, or a bit lip or tongue
are the most common causes.
3) Blood capsule. This was non-existent ten years ago
but has come into use recently. The blood capsule (or, more likely,
a condom filled with fake blood), is primarily used when a wrestler is
supposed to have "internal bleeding." Since blading can't really
portray that, they use the capsule. Like with blading, the camera
will usually cut away from the wrestler for a few moments while they bite
down on the condom.