"Shag Balls"

I 100% regret my decision of teaching my teammates and coaches the term "shag" (which just means go get the balls and put them in the cart or basket). Because my coach now uses the phrase "shag balls". And my dirty little mind is either laughing or disgusted every time I hear it. So this makes me wonder why we use the term shag. It used to seem so normal and natural, but now I always think of Austin Powers and dirty dirt dirty! My mistake.