A WebmasterWorld thread says this ban is brand new. He has had ads for that keyword phrase for a long time and now Google is telling him that these ads are not a "good match for AdWords". Even if you sell sporting goods for horse racing, or horse racing toys or anything not related to the gambling side, you cannot bid on the term [horse racing] (you can bid on [horse racing toys]).
Senior member, woop01 said:
We have been told by an Adwords rep that now horse racing and horse racing related activities are no longer considered a "good match for Adwords". I'm not talking about the wagering aspect of horse racing, the entire sport of horse racing.
We spent an afternoon removing any of the very minor references to wagering on a horse racing site that had been advertising with Adwords for years. Unfortunately, it was only after we did it that the rep then said that horse racing in general is the problem.
I find the whole thing fairly interesting.
Forum discussion at WebmasterWorld.