Idk about the specific rule, but I'm guessing it's got more to do with the downward elbow movement than the region being hit. Definitely a more dangerous attack, and it's also usually only possible if you're in an advantageous position.
As for the region being hit and rules, punching is legal in boxing, but that doesn't mean you can go speed bag on someone's balls.


Discord, lol... At least use matrix if you're going down the road of suboptimal communication.