This has only a few crochet in it. I saw this upcycling idea somewhere on the Internet.
You cut the lower part of a shirt into ribbons, then you knot. It gets more and more narrow the more rows of knots you make. But jersey is stretchy, so I don’t have problems to put it on.
I didn’t like the round neck. I cut a hole and crocheted a small stripe in Tunisian crochet which I crocheted together after pulling it through the hole.