What happened in Valencia 2015

I'm new to MotoGP and new to riding in general, I was watching Rossi's Lap of Honour in Valencia 2015. While I was scrolling through the comments, I saw a lot people say that they won't forgive what Marq did to Rossi there. So just what did Marquez do? I'm aware that Rossi was only 5 points behind JL99, the Champion was determined by that round, and that it would have been Rossi's 10th Champion, but why all the hate towards Marquez.

I'm new to MotoGP and new to riding in general, I was watching Rossi's Lap of Honour in Valencia 2015. While I was scrolling through the comments, I saw a lot people say that they won't forgive what Marq did to Rossi there. So just what did Marquez do? I'm aware that Rossi was only 5 points behind JL99, the Champion was determined by that round, and that it would have been Rossi's 10th Champion, but why all the hate towards Marquez. http://ifttt.com/images/no_image_card.png