I would like to chime in on your entrepreneurial idea. I think you have a great idea, athletic fitting golf shirts! It is a niche market but that's what makes it a good opportunity. Although, after reading all the other posts to your tread...I like some of the others ideas of fitting a average, yet taller or broader build of individual, especially in a style of shirt that fits and is produced with 100% polyester or other microfibers! Please don't get me wrong, by all means run with your idea I think it's great.
For the last year or so, I've been reading treads and doing my own research on most of these topics discussed here. The market has plenty of room for more apparel, especially if priced in the $20-$40 range and good quality. I'm in the final stages of finishing my website that will accommodate a wide variety of golfers, male, female and children, as well as varying styles of golf clothes...Shirts, windbreakers, fleeces, mock T's etc...All the while keeping body symmetry as the number one priority.
I have located and contracted a very reputable apparel wholesaler that has agreed to drop ship the merchandise for me once I place an order. I have tested the market with some of the shirts and the response has been overwhelming. The apparel is 100% polyester or spandex 70/30 split. I started doing this on the side to make a couple extra dollars to help with my golf rounds and the idea has grown and spawned different avenues!
I think your idea is great and apparel is easily marked up 300%, but at a 50% mark up the sky is the limit! If you already have a supplier than kudos for you...If not, we can chat and maybe we can put something together.