West Brom were losing to West Ham and Mulumbu didn't like that because he hates losing, so when Gary O'Neill tripped him up he did what any grown adult professional footballer would do in a similar situation. And by that I mean he picked up the ball and kicked it at him as hard as he could.
The closest thing to this I've ever seen was when some guy in my junior team (we were 15) threw a throw in off the referee's head because he thought it would be funny, and it was funny, until he was sent off.
The difference here is that that guy was 15, and Youssouf Mulumbu is like 28 or something. Also it's his job. It's like if you threw a cheese burger at someone at your job. Hah aa ha ha a i insulted you so bad