One of my friends relayed this story to me that happened to him a few weeks ago. He was playing at one of the better public courses in the area. His group was walking off the green but not quite off it when one of the guys in the group behind them went ahead and hit his shot to the green. My friend said the ball landed not 5 feet from him. My friend picked the ball up and went to question the guys in the fairway. They gave him the story that he didn't know he could reach the green. They were only 150 yds from the green. He said there was almost an altercation in the fairway between the two foursomes before cooler heads prevailed.
I know the group he plays with so I know slow play from his group wasn't an issue. Rounds on this course do typically take longer than normal due to the course being busy.
So how would you handle this situation or your own situation should someone hit their approach shot to the green you are walking off of?