The shorter the better for freeballing. BOA USA makes a pair of split leg running shorts with a 1 inch inseam which is the shortest of any running apparel brand.
Has anybody tried them?? Let me know.
Because I figure it's got to be impossible to keep your cock and balls from slipping out constantly. And especially if you take the liner out. I'm going order a pair soon. I'm also attaching some pics from their site so you can see them.