Actually, with cue ball in hand after a scratch, your opponent can't place the cue ball in the pocket and foul by using the tip of his cue to freeze the cue ball against the inside of the corner pocket....because, the cue ball is not in play for a legal shot or foul until AFTER it has crossed the head string foul line, and until that happens, no shot has taken place because the cue ball is still out of play after a scratch.
That always struck me as odd.
So then while one is preparing to shoot and taps the cb with the tip, it isn't a foul...unlike how it would be on any other shot?