Also perhaps related -- "scratch" can be a sports term, particularly in horse racing, meaning that the athlete's participation in the event is canceled. So, you start over from scratch because the other thing went wrong. In the sports situation, I imagine other competitors or bettors at one time noted scratches that were denoted by a line drawn through the canceled person's name. The athlete was "scratched out." I suppose this goes beyond sports -- "we had to scratch our plans." There is also a "scratch golfer," meaning one that has no handicap.
Also perhaps related -- "scratch" can be a sports term, particularly in horse racing, meaning that the athlete's participation in the event is canceled. So, you start over from scratch because the other thing went wrong. In the sports situation, I imagine other competitors or bettors at one time noted scratches that were denoted by a line drawn through the canceled person's name. The athlete was "scratched out." I suppose this goes beyond sports -- "we had to scratch our plans." There is also a "scratch golfer," meaning one that has no handicap.