Blink and you might have missed it. Even viewing replays from the other angles UFC afforded us to watch, opinion varies on the legality of Anderson Silva's knee against Chael Sonnen during the main event of UFC 148, and is especially dependent on what quality and speed you watch the replays in. Officially, referee Yves Lavigne did not call the knee illegal, and the replays were enough to satisfy the UFC broadcast team of Joe Rogan and Mike Goldberg, as well as UFC president Dana White. The knee hit Sonnen's chest, case closed.
Well ... not quite. Watching the replay myself at various speeds in the best quality available to me, it seems clear that the point of Anderson Silva's knee did not hit any part of the head of a seated Chael Sonnen. As best as I could make out, the point of the knee hit the top of Chael Sonnen's chest, from anywhere between the Suprasternal notch to the mid-sternum (or there abouts). That's the point of the knee, though.
Because of the anatomical V shape a bent knee makes, the upper side of this V -- where the front quadriceps meet the top of the knee -- can make contact with an opponent's head before or during a strike aimed at the upper chest, because of how the head naturally protrudes beyond the upper chest. And in the case of Anderson Silva, this upper side of his knee has to make contact with the head of Chael Sonnen for the point of his knee to land where it did on Sonnen's chest, and this incidental blow to the head is exacerbated as the fence prevented Sonnen from recoiling back on impact.
Some might question whether it matters if the lower thigh made impact with Sonnen's head, because it wasn't the point of the knee and so wouldn't have done as much damage, but I think the point is being missed with this attitude. We know padded gloves protect the hands of the fighter throwing a punch, and not the opponent receiving it, so arguably the natural padding of leg muscle benefits Silva more than it does Sonnen. Even if you don't want to buy that argument, if a roundhouse kick was thrown at the head of a seated Sonnen, but only the thigh makes contact while the point of the knee, shin or instep miss, it would still be deemed as a kick to the head of a downed opponent.
Others might be quick to point out the intent is different, with Silva's intent to hit the chest, and the head of Sonnen ended up being collateral damage. But even inside leg kicks that land on the inner thigh but ride up into the groin more often than not cause a fight to be paused by a referee, who will give the opponent time to recover, even though the intent was to kick the leg.
Yves Lavigne didn't call the knee Anderson Silva threw against Chael Sonnen illegal, but that doesn't mean the call was correct. It's also an incredibly tricky call to make without pausing the action and to check the instant replay (which NSAC approved the use of nearly 3 years ago), or without better slow motion cameras on hand.
I won't speculate whether the knee being called legal or illegal, and Sonnen given some time to recover would have made any eventual difference to the outcome, as that's largely irrelevant to this article. I honestly didn't care who won last night. But because this situation is such a gray area, I'd either expect fighters to exploit it a lot more and point to the Silva vs Sonnen II fight as a precedent, or referees and commissions to step up their game and use instant replay to help make a call.
Of course, it'd be a lot simpler if we just legalised knees to the head of a downed opponent.