Shut up, cretins everywhere
Point 1: Kaka clearly, obviously, makes an active short jabbing motion with his elbow towards Keita's chest.
Watch the video by clicking the pic above and then clicking the "RED CARD" clip, particularly from 0.36 to 0.38. Watch Kaka's arm. I think the mistake people have been making so far is to watch the footage with their eyes closed and their brains replaced with a turnip.
Point 2: Watch Kaka's reaction. Is he surprised that someone's bounced off him and fallen to the ground? No. He knew Keita was coming and he did something about it. Note, incidentally, that at NO POINT does Keita look towards Kaka as he runs. He's watching the ball, not looking for a foul.
(He couldn't sensibly expect to get one even if he was, because at the time he can see that the ref is looking in a completely different direction from Kaka and him, and both linesmen are at least 60 yards away.)
Point 3: Look at how Kaka is standing in the first pic on this page. That's not someone standing around unsuspectingly being collided with from behind. Had Keita collided with him in this position, if Kaka wasn't moving his centre of gravity backwards at the time (for example, jabbing his elbow towards the Ivorian), he'd have been sent flying onto his face.
Point 4: Kaka doesn't then stand around looking surprised and confused when the furore blows up. He jogs off, as fast as decency allows, getting as far away as he can get from the situation, and hamming exaggeratedly to the bench that he knows nothing. As any remotely competent psychologist will tell you, it's absolute textbook guilty behaviour. Go on, find one and ask them.
Point 5: Keita's face-clutching at first seems reprehensible, but we can clearly see from the replay (at 38 seconds) that the left side of his head collides pretty forcefully with the side of Kaka's head (and/or possibly Kaka's shoulder), so he probably genuinely is in considerable pain. He certainly puts his left hand to that exact point of impact.
He's not playacting – he's just had a hefty bang on the noggin, regardless of whether anyone hit him there deliberately or not. (And Kaka certainly didn't deliberately hit him on the head. But that lack of intention doesn't mean Keita hasn't been genuinely hurt in the head.)
Even if he was faking it cynically, or just exaggerating a bit… well, welcome to karma, Brazil. And in any event it doesn't forgive Kaka elbowing him in the chest, which is a clear yellow card offence at least.
And let's remember, these hopeless BBC pundits and commentators who've started the Keita witch-hunt are the same ones who watched the slow-motion replay of Luis Fabiano's goal from the angle below and said "A suspicion of handball there? No."
Seriously, everyone, just shut the fuck up.