Nevermind the controversial and comical free kick that led to Liverpool's first goal (some claim this is "beach ball karma"), the following four freeze frames show an important refereeing decision that needed courage to convict the offender. This was when Liverpool’s Steven Gerrard jumped up and into Sunderland’s Danny Welbeck (and clearly led with his elbow).
[Steven Gerrard (red #8) leads with his elbow and makes contact with Danny Welbeck's face (white #17). Gerrard also missed the ball.]
[Referee Stuart Attwell is well positioned for this incident]
From the above freeze frames, 27-year-old referee Stuart Attwell is well positioned to see Liverpool’s Steven Gerrard jump up and into Sunderland’s Danny Welbeck. Gerrard's forearm and elbow make contact with Welbeck's face , and any contact between hard, bony objects (i.e. elbows, forearms) and soft, fleshy surfaces (i.e. face and neck regions) is dangerous. Also, Gerrard doesn’t make contact with the ball.
Referees are taught, trained and advised to give red cards for these offences, so it was surprising that Attwell only cautioned Gerrard.