Hey all,
Thanks for the responses. I did find another passage regarding uniforms:
Rule 3-5-3 - "Equipment which is unnatural and designed to increase a player's height or reach or to gain an advantage. Equipment shall not be modified from it's original manufactured state and shall be worn in the manner the manufacturer intended it to be worn"
I'm looking through the whole section on uniforms and none of the rules (except the one on numbers and the one above) seem to apply. However, if I understand everyone correctly, unless the rest of the kid's team wore their uniforms backwards, what he is doing is "illegal".
Thankfully, no one in the league has worn their jersey upside down.
Thankfully, this is just rec league. However, things still come up and I get to think about it and improve my rules knowledge (which needs a lot of work