Elbows and knees are strikes thrown from the body's hardest, sharpest joints, and fighters reach for them specifically because punches and kicks don't work as well at very close range — inside a clinch, against the cage, or in a scramble on the mat. An elbow can open a cut that ends a fight on a doctor's ruling even when the fighter throwing it never comes close to a knockout, and a knee thrown up the middle or into the body can end a fight outright. Both are legal everywhere on a standing opponent's body, including the head, but knees (and kicks) to the head of a grounded opponent are illegal — a rule that has moved in the last two years and now depends partly on which commission is overseeing the card.
What makes an elbow different from a punch
A punch lands with the flat knuckles of a closed fist. An elbow lands with the point of the ulna, the forearm bone that comes to a hard edge at the joint, and concentrates the same force into a much smaller area. That's why an elbow that would barely stagger someone can still split skin open on contact.
Fighters throw elbows on a few different lines. A horizontal elbow slices across, the way a hook does, and is the version you'll see most often at punching range or in the clinch. A diagonal or upward elbow travels at an angle, often uppercutting through an opponent's guard as they close distance. The straight-down version — thrown from a raised elbow crashing directly downward onto a grounded opponent, nicknamed the "12-6" for its clock-face trajectory — has the most complicated legal history of the three: it was banned for most of MMA's modern history, legalized under a mid-2024 update to the Unified Rules, and, because every state athletic commission has to individually adopt that update, still isn't legal everywhere. What's actually illegal in the UFC covers that patchwork in more detail, including the related change to what counts as a "grounded" opponent.
Why elbows produce so many stoppages by cut
Doctors stop far more fights on cuts than most new fans expect, and elbows are the biggest reason why. The skin around the eyebrows, the bridge of the nose, and the scalp is thin and sits close to bone, so a small elbow can open a laceration that bleeds heavily and obstructs vision even when the underlying damage is minor. A ringside physician who judges a cut too severe, or too close to the eye, to safely continue can end the fight regardless of how either fighter is doing on the scorecards — which is why a single well-placed elbow in a clinch exchange can change a fight's outcome as fast as a knockout blow.
Knees: the same principle, applied with more force behind it
A knee strike works on the same logic as an elbow — a hard, pointed joint replacing a softer striking surface — but with the added mass and leverage of the leg driving it. Knees are thrown in two main settings. In the clinch, a fighter controlling the back of an opponent's head or neck (a grip commonly called the "Thai plum," borrowed from Muay Thai) can drive repeated knees up into the body or head with the opponent unable to retreat. From a distance, a fighter can also throw a knee as a leaping strike closing the gap, usually aimed at the head or chest as an opponent moves forward.
Knees to the body carry a specific reputation among fighters: a knee that lands squarely on the liver, on the side of the torso just under the ribs, can cause a level of pain that drops a fighter regardless of conditioning or toughness, in a way body punches usually don't. That's distinct from a leg kick, which targets the thigh or calf rather than the body or head and is thrown with the shin rather than the knee joint itself — a separate technique covered in leg kicks and calf kicks, explained.
The rule that matters most: grounded opponents
The one hard limit on both weapons is the same limit that governs a lot of MMA's rulebook: what a fighter can do once an opponent is considered "grounded." Under the Unified Rules, knee and kick strikes to the head of a grounded opponent are illegal, though strikes to the body and strikes with punches or elbows to a grounded opponent's head are generally allowed. The definition of "grounded" itself changed in the same 2024 rules update that legalized the 12-6 elbow, and — because adoption isn't universal — a fighter who is technically grounded under one state's rules might not be under another's at a different event. A fighter who throws a knee or kick to a downed opponent's head under the old, stricter definition, at an event still running the old rules, can be penalized or disqualified for a strike that would be perfectly legal a few weeks later at a different commission's card.
Where to watch for them
Elbows and knees show up most often in exactly the spots where punches get crowded out: fighters trading in the pocket at close range, pinned against the cage in a clinch, or scrambling for position on the ground. A fighter who is losing a striking exchange at distance will frequently look to close that distance specifically to create elbow and knee opportunities, since a clinch neutralizes an opponent's longer weapons while opening up these shorter ones. Watching for a fighter deliberately closing distance, rather than backing away from pressure, is often the clearest sign that an elbow or knee is coming next.
The practical takeaway: elbows and knees aren't just smaller versions of punches and kicks — they're a different category of weapon that fighters use specifically because the range dictates it, and the rules around them (especially near the ground) are stricter and less uniform than the rules governing striking anywhere else in the cage.