like a previous poster said they were watching the shot. They knew where it was supposed to go. You got screwed.
I beat a guy in a singles qualifier once. In the last rack I marked the pocket with a piece of chalk. My opponent notices another piece of chalk on the table near the othe corner pocket and tried to protest that I marked the other pocket, and put the 8 in the wrong pocket. The tourney director did the right thing and the guy then tries to shake m hands and says "Good game anyway" I wanted to tell him to go F himself, but I just walked away instead....
This, in my league area, is a rare event. Most of the folks in our division aren't nitty like that....