Fersis said:
How the hell is that legal ? He could broke the guys arm.
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EDIT:Its broke or brake? Broken English FTL!
That's what submissions are - physically pressuring the other guy until they give up. Pretty much every single one will lead to either something breaking or the other guy going unconscious if they don't tap or the ref doesn't stop it. It's very rarely the case when something goes wrong, but it has happened. Most fighters aren't looking to significantly injure their opponents - injuries are just a by-product of the sport, albeit quite rare considering what the sport involves.
Most often, guys will tap when they're not necessarily in pain if the guy has locked the submission in, because it usually isn't worth the risk to linger in it.
Several moves are illegal, i.e. moves that involve the small joints. Meaning, you can't grab someone's finger and just start twisting it.