Late in the second half of Saturday's match between Chelsea and Sunderland, Sebastian Larsson barged into Ramires while he was going up for a header right in front of an empty net, denying him a sure goal. Referee Mike Dean didn't see anything wrong with Larsson's challenge and let play continue. Ramires was probably upset about this and decided to react by smacking Larsson in the face about a minute later.
If this doesn't show up in Dean's post-match report, Ramires might get a retrospective ban. While he's not in the best of form for the Blues, it would still be a massive loss for the rest of the season, given that Chelsea are still in Champions League. They need all the bodies they can get.