I had a PC want to sneak up and slit the throat of a Gamorrean guard. I had him roll a stealth check and then an athletics check for the kill. I decided because it was a surprise attack the actual wounding was in the bag, but whether or not he'd succeed in leaping up and getting his arm around was something that required a roll. Though ultimately he succeeded he also had threats, so I had the guard hit the ground heavy, alerting other guards in the area.