I use this approach in all leagues. Your ultimate goal whether you like to admit it or not should be to win. In my house shot league now, there are a large gap of bowlers, some that average 230 and some that average 130 and a lot in between. So, when I am up against a stacked team that has an average game of 1100, I like to do what I can to help my team and hurt the other team. I take a sanded down Fear Factor, sanded with Storm's red scuff pad, a ball I only use on the oilest of conditions because I can make the ball do anything I want as far as hook goes and use it in practice to break in a groove for the other players on my team that like to play similar lines to me, which is 2 of them plus me. We all like to play the outside part of the lane, which means use 5 as our breakpoint. So, I try to keep the oil out there and not break it down by playing inside of that in practice where most of the other team plays, which is usually around 10. So, I will throw the Fear Factor with a lot of hook and straight down to slop around the oil so it breaks down quicker and forces the other team to move. Then what I will do is take that ball at the end of practice and throw it in my own line and start to make a groove. The other players groove who are around 10 has already started to break down and my groove is starting to get grooved when practice is over.
So, to answer the questions, no none of those ways are illegal or unethical, it is simply to gain a competitive advantage on the other team. In bowling gaining a competitive advantage in practice is not illegal.
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If you are not using Storm, go kick yourself hard!!!