The following acts are universally considered fouls in the mixed martial arts world:
- Head butting.
- Eye gouging.
- Hair pulling.
- Attacking the groin.
- Strikes to the back of the head and spinal area.
- Strikes to, or grabs of the trachea.
- Small joint manipulation (control of three or more fingers/toes is necessary).
- Intentionally throwing your opponent out of the ring/cage.
- Running out of the ring/cage.
- Purposely holding the ring ropes or cage fence.
- Grabbing or putting a hand inside the trunks or gloves of the opponent.
In N. America you cannot knee or kick a downed opponent (knees on the ground or lower) in the head (i.e. no soccer kick). You cannot stomp down on a downed opponent or jump feet first onto a downed opponent.
The fact that there is no standing count (such as in boxing) prevents people from taking horrendous amounts of abuse such as in boxing where a man's head can get pummeled over and over and over and as long as he gets back up and stands on his own before the count is up he can go back in and have his head bashed on over and over and over. Getting knocked out swiftly is typically going to be less damaging to you physically than having your skull rattled around forever. All in all I think people are more likely to get severely injured in traditional boxing than they are in MMA. Think of all the matches that end in a submission or G&P which isn't always as painful as it looks, but once you lose control and the ability to defend the ref calls the fight. In boxing the goal and only real goal is to pound your opponent in the face until he cannot go on.