Manchester United is out of the Champions League. They were in the lead 1-0 when Nani was ejected from the game for allegedly hitting Arbeloa in the chest with a flying kick. But playing back the video, you don't really see a whole lot of contact.
It was an immediate red card. Real Madrid went on to score two goals to win 2-1.
Here it is in GIF form. The red card was harsh, and it changed the outcome of the game: