Your goal in SC, when answer A is wrong, is
not (as this "official explanation" seems to claim) to find the answer that makes "the fewest unnecessary changes" to the original. If A is wrong, the original sentence is wrong, and if an SC answer is wrong, it usually doesn't have a sensible meaning, so there's no reason to try to preserve it. There's no basis to choose between C and D here, and E looks fine too, so it's not a well-conceived question. And when the official explanation says "
oftentimes is not a mistake", that might technically be true, but you'd almost always want to replace that word with "often", which is shorter and means the same thing. You also can't use the preposition "in" in this sentence at all, so every answer choice is wrong; you can talk about the audience
at a soccer game (among other possibilities), but unless the audience is actually taking part in the soccer game, you cannot use "in" here.