Humans are one of the few species that are bipeds. A lot of interesting anatomy comes from this evolutionary divergence. In MMA one such advantage is the leg kick. It has taken on an interesting evolution in this fledgling sport and Forrest Griffin's victory over Quinton Jackson was simply the latest chapter.
Mirko 'Cro Cop' Filipović is the fighter that first comes to mind once the phrase leg kick is muttered. Mirko was a kickboxer and took those skills into K-1 and PRIDE. His leg kicks were predominately to the head and achieved devastating force, don't take my word for it, check out the highlight reels on youtube. The force was such that Mirko 'Cro Cop' was purported to say "Right leg, hospital; left leg cemetery." Indeed that was the case for him. Ironic that the master of the leg kick was taken down by one from Gabriel Gonzaga. Cro Cop has since fallen off the path. Where as Gonzaga used those same kicks with a fight against Randy Couture. During the fight Couture broke his arm deflecting one such head kick, yet still went on to convincingly win the fight.
While the leg kick is often thought of for its devastating knock out ability; Griffin showed us that it fits in to a well thought out game plan. Not to say these leg kicks aren't powerful, Forrest did break a VP's leg with one such kick. This recent trend to use leg kicks to weaken your opponent didn't start with Griffin or really any fighter in particular. Keith Jardine employed it to great effect in his win over Chuck Liddell.
Lyoto Machida uses a host of accurate leg kicks from different angles throwing off his opponents balance allowing him to control the fight. Miguel Torres knows the value of bludgeoning an opponent's sciatic nerve and thigh. In his recent fight with Yoshiro Maeda, Torres struck Maeda's thigh with his heel every time in guard.
These fighters showed how valuable the leg kick is in order to be a well rounded fighter. Constantly chopping down on an opponent's leg with kicks causes more than just pain. It also decreases mobility and keeps separation; something that Jardine and Griffin both used to great affect in their upset victories. The distance created allows the fighter to keep the initiative in order to set up combinations. Once again exemplified in Forrest's victory.
How to stop such a methodical tactic. Go to the ground on your terms. Something that Liddell and Jackson failed to do in their loses. The repetitive nature of these leg kicks is a weakness. If a victim of such an attack grab the leg kick and take your opponent down. Because Liddell and Jackson failed to adapt in time, they lost their fights.
Young fighters pay attention, know how to both use and defend the leg kick it can be the key to victory or defeat.