UFC loves rules. Fighting has to have rules or else we’ll just have guys murdering each other for entertainment purposes. That sounds pretty uncivilized to me! So the following things are considered fouls in a UFC fight: biting, eye-gouging, fish-hooking, groin attacks, small join manipulation, hair pulling, putting a finger into any orifice/cut/laceration, throat strikes, grabbing the trachea, clawing, pinching or twisting the flesh, grabbing the clavicle (until recently), intentionally attempting to break the opponent’s bone, kicking to the kidney with the heel (until recently), spiking an opponent to the canvas on the head or neck (piledriver), throwing an opponent out of the ring or area (this ain’t WWE), holding the shorts or gloves of the opponent, spitting, engaging in unsportsmanlike conduct causing injury to the opponent, holding the ropes/fence, using abusive language within the ring/fence, attacking an opponent during a break, attacking an opponent who is under the care of the referee, attacking an opponent after the bell has sounded the end of the round, flagrantly disregarding the instructions of the referee, timidly avoiding contact with the opponent, interference by the corner, using any foreign substance that could give an unfair advantage, head-butting, striking to the spine or back of the head, and striking downward using the point of the elbow.
I like having rules, structure, and limits and knowing that those opposing me are being held to the same rules, structure and limits. This is another hugely attractive element of the UFC to me.
And there is match conduct rules which I find valuable in validating the sport. After a verbal warning a match can be stopped by the referee if they reach a stalemate on the ground, this keeps the action moving and keeps everyone interested. If the referee pauses the match, it is resumed with the fighters in their prior positions so the ref can’t pause based on allegiance with either fighter. And it is preferred that trash-talking be limited to prior and following a match so that the match itself is about the fighting not the mental mindfuckery!