it was almost the perfect break -- he sank the 8 on [the snap], but still lost due to the pocket scratch
"the term "scratch" is often heard around a game of pocket [billiards] (or [pool]) to represent a foul in which:  1
"it was almost the perfect break -- he sank the 8 on [the snap], but still lost due to the pocket scratch" What is the definition of "scratch"?