Use NFHS case book play 10.3.7 for guidance. That one refers to a thrower hitting a defender in the face with the throw-in. Jmo, but hitting him in the nuts should be considered the same(or worse
).
The case play says that the administering official will have to determine their call based on:
1) Was the throw-in to B1's face accidental or a voluntary, planned act?
2) Was the ball contact caused by the movement of the defender?
3) Was the act of an unsporting nature?
If you feel that it was accidental or that the defender moved into the path of throw-in, the only call would be to repeat the throw-in if it went out of bounds.
If you felt that the the act was deliberate and malicious, you can call either a technical foul on the thrower(using 4-19-5(b)-->a non-contact foul by a player....or 4-19-14), or if you felt that the act was an attempt to injure--> a flagrant technical foul(using 4-19-4--> non-contact which is extreme).
It has to be be a technical foul because there was no physical contact between the two players. All personal fouls involve contact.
Personally, if I felt that the thrower deliberately hit a defender in the face or balls with a throw-in, I'm calling a flagrant "T".