I have to agree. If you purposefully use a ball in which you may not score as well as you would with another, that is a form of sandbagging. I know people who only bring a white dot to league and average over 200, even though they throw aggressive stuff in tournaments. Don't get me wrong, I don't mind losing to someone with a white dot, but to do that and get handicap on top when you would be a 230 bowler with anything else, just isn't right.
But I also realize people don't bring every ball they have to league. You may bowl bad and say, "I could have used ball X and shot much better tonight," but don't ever admit to laying off on purpose.
I guess, just admit to using a different ball to keep your average down.
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I am not a pro-bowler, but I do play one on BallReviews.com