I currently run a hoodie website (www.infinityhoodies.com), and I'm strongly considering mixing print on demand products with dropshipped parkour apparel to create a parkour business. What do you think about the niche in general?
If it's print OD, you're in a great position for low cost testing - just fire up a few designs and run some Google Ads + maybe a little FB traffic straight to the product pages and see how they convert.
That data will give you a better answer than opinions :D
I personally like the niche (and youtube videos!), but haven't tested so I don't know how it would perform.