Sure, a teammate of the thrower can go OOB to receive a pass from the thrower and then inbound the ball. How is that unauthorized?

I think we are saying the exact same thing, getting wires crossed somwhere...I'll just say that I agree, that IS authorized....

Thanks for the answers everyone.

During an endline throw-in following a made basket, a teammate of the thrower would be leaving the court for an authorized reason. A player in-bounding a ball is also out of bounds for an authorized reason. Therefore, no exception would be needed

I suppose the exception would need to be stated for the made-basket/end-line throw-in, for clarity. Not precisely an exception, but a clarification of "authorized reason."

A teammate out of bounds on a spot throw-in doesn't need a separate rule, because that's an unauthorized reason.

Authorized reasons typically include momentum. The rule for throwins simply indicates there is no such thing as an authorized reason during that time.

Right.

If leaving the court for an unauthorized reason is already a violation, then theoretically a separate rule stating no teammate of the thrower may be out of bounds during a spot throw-in would not be required. A teammate of the thrower is not authorized to be out of bounds during that situation, therefore he left the court for an unauthorized reason, therefore violation.

Except that an authorized reason would be momentum, right? But on a throw-in, even going OOB for momentum reasons is a violation.