I can't say always, but very often it is. I read an article about this a while back. Turns out that when you're exerting and hot and sweaty like these guys, a tiny cut in the right place, like on the forehead at the hairline, will produce a scary looking, but inconsequential, stream of blood, with no significant pain or risk. Some people's body chemistry makes them really good bleeders. So they do very often have with them the means of making the cut at the right dramatic moment. The wrestlers are essentially stuntmen. What they're doing is difficult, physically demanding, and dangerous, even if the risks are controlled and the fights are mostly optical illusions. Pain and blood are a fact of life for them, and they take it in stride, as a pro football player would.