I think the reason he scratched is that he had to cut the 10 slightly to the left to be sure it got under the 13 rather than coming off the 13 toward Red's pocket, which is what I would have been afraid of.. He got down on a short table shot twice, then pulled up. He ended up following the 10 ball, trying to place the CB up by the far corner pocket. Unfortunately the aim or speed was a smidge off, which caused the CB to scratch in the pocket by which he wanted to leave it.
You're right. I'm not sure why he chose that shot, although he might have believed that Red wouldn't shoot the 11 (by Red's hole) from the position of the upper pocket.absolute disaster shot for bob there. as he gave up a real chance of winning for a shot that does little and a sellout that cost him the game.