Even Sportscenter was running this video, so its entirely possible that you've seen it already. But if you haven't, and you've played any soccer in your life, prepare to wince a bit. I'm shocked that this doesn't happen more often, frankly. Getting a kick right in the head is in fact exceedingly rare--I've seen a boatload of close calls. But this is pretty much straight on. Clearly an accident--Abou Diaby certainly doesn't look to be trying to do anything but a clear a dangerous ball out of his zone. But scary. John Terry is OK, reportedly. He says he doesn't remember the kick, which is hardly shocking.
Our friends at Sanford Soccer Net showed me the way to the Youtube vid. Chelsea did go on to win this thing. Sanford's got the video of the goals (and the brawl).