UFC welterweight demigod Georges St. Pierre, in a rare display of humanity, tore his ACL and will be out at least nine months, and as per Dana White, while the Canadian champ recovers, the other alphas of the 170-pound division will fight over an interim title like dogs over table scraps. Boy, that injured knee sure is a game-changer, no? With one hyperextended joint and torn ligament, St. Pierre has managed to upend an entire weight class. Now Nick Diaz – who was to face the champ at UFC 143 – will face Carlos Condit for a shiny belt that has only a fraction of the value of the one St. Pierre possesses, and others will scrum to determine who gets the next crack at the faux-championship. Of course, such sudden and surprising shifts in the Octagon paradigm are nothing new. In fact, the notion of an injury altering the course of a group of fighters’ trajectories is something we’ve had to deal with since almost the very beginning of mixed martial arts here in the States. So here, without further ado, are the top five instances of when a fighter’s unexpected injury screwed up not just himself, but a whole mess of other people as well. Holy game-changers, Batman!

-Royce Gracie – It was hard to swallow that a skinny Brazilian dude could cut through a field of massive, muscular and frightening martial arts experts, but that’s what Gracie did at UFC 1, and we accepted that as maybe some kind of fluke. Then he repeated the feat at UFC 2 and the idea of his victory being an aberration faded. So it was that Gracie entered into the tournament at UFC 3 as the man to beat, with chief foil Ken Shamrock waiting patiently in another bracket and quarterfinal opponent Kimo Leopoldo looming in what should’ve been an easy fight for the grappling master. But Kimo pounded the crap out of Gracie, and though the Brazilian eventually earned the tap out, the two-time UFC tournament winner was spent. His “injury” was actually dehydration, although later on he also blamed neck and shoulder issues. Gracie had enough energy to get dragged back to the locker room, then get dragged back out, at which point brother Rorion threw in the towel. You think that threw a wrench in the whole Gracie-Shamrock works? You bet it did, and it opened the door for Shamrock to bow out of the UFC 3 tournament and for alternate Steve Jennum to come in at the finals and win the whole damn thing. Ugh, what a clusterf**k.

-Tito Ortiz – If anyone is good at mining the potential of a grudge match, it’s former light-heavyweight champ Ortiz, who pretty much squeezed every dollar possible out of a fabricated rivalry with Shamrock, and then attempted to do the same with Chuck Liddell, milking a trilogy out of what should’ve been maybe one fight in the Octagon and then some harsh words on Twitter. But no. Ortiz convinced the Powers That Be that there was value to him fighting Liddell a second time, and that hey, wouldn’t it be great if he and Liddell were opposing coaches on the eleventh season of the Ultimate Fighter and then they’d fight a third time? Sorry bud, it would not be great. Multiple herniations in the neck of the “Huntington Beach Bad Boy” would see Ortiz pulled from his coaching spot late in the taped season and booted from the show. His replacements in the final episode were Rich Franklin, Forrest Griffin, Tyson Griffin, Gray Maynard and anyone else standing in or around the Xtreme Couture gym in Las Vegas on that particular day of shooting, and forevermore SpikeTV executives would lament about all the film they wasted on a pushing a bout that would never come to fruition.

-Frank Mir – Despite one hiccup against Brit slugger Ian Freeman, Mir was for a while the hottest and most promising heavyweight on the UFC’s roster, and everything came together for him when he took on Tim Sylvia for the belt and snapped Sylvia’s arm. Hooray, a new and exciting champ! But then came a horrific motorcycle accident, and the Las Vegas native’s leg was shattered – an injury that took so long to heal, Sylvia and Andrei Arlovski fought for an interim title that eventually morphed into a real title when it became clear Mir would need a lot more time before coming back. (And when he did come back, he was a shadow of his former self; it would take almost three years for the badass Mir to return.)

-Brock Lesnar – I’d never even heard of “diverticulitis” before Lesnar was felled by it, and the Human Mountain has had it affect his career in the Octagon (and the careers of the other big boys of the division) twice. The first time, Lesnar was champ and was to defend his belt against Shane Carwin. That idea got kicked to the curb with a quickness, and Carwin ended up facing Mir for the interim belt. The second time around it struck when Lesnar was coaching TUF 13 opposite Junior dos Santos, a turn of events that had Carwin taking on the Brazilian instead and SpikeTV execs once more smashing their Blackberries in disgust and anger.

-Ken Shamrock – Maybe Shamrock really was sparring too hard the day of his scheduled EliteXC bout against Kimbo Slice, and the cut above his eye was inadvertent and legit. Maybe not. Either way, on the night of what should have been EliteXC’s fiscal wedding day to CBS, Shamrock’s injury opened the door for Slice to take on the smaller Seth Petruzelli. We all know how that played out, and soon after, EliteXC was no more. Now THAT injury was a game-changer.