Whether it be a vicious elbow, an unintentional hit, or a light grazing, depending on your point of view, Wayne Rooney has made contact with the face of David Luiz and as a result, has been shown a yellow card. Some may see it as a straight red card, as it appeared that elbow met grill, but Rooney also looked to attempt to avoid Luiz after jumping towards him when he realized he wasn't going to win the ball. It was much more stupid than it was malicious, but it's hard to determine intent and unfair to take it into consideration when contemplating a sending off.
Branislav Ivanovic, who is on a yellow card, also narrowly avoided sending off minutes later, in the 41st minute, as he made a cynical challenge from behind on Rooney. Howard Webb opted not to show a yellow card, keeping it in his pocket on the second occasion on which he could have easily sent off Ivanovic.