Relative to the discussions in the past week or so regarding double punishment, I think there was an example of this in last evening's MLS game, Dallas Vs. San Jose.
In the 90th minute, a defender "elbows" a retreating attacker in the back of the head, dropping him in the far corner of the PA 17.5 yards from the goal line. The referee has his back to the "action", having turned to follow the counter attack up field, but the AR sees the action, get's the referee's attention, and they have a small conference. The PK is awarded. NO CARD, conceivably direct red for striking, certainly yellow for USB, but then, that would have been the defender's second yellow, requiring a send off, so the decision is that the PK is enough punishment, no misconduct.