Where is Throw in?
 

A4 has a throw in from baseline. He throws it to A2 who catches the ball about 15 feet away on the sideline. A2 has one foot on the sideline when he catches the ball.

Question: where does the throw in for team B take place?

Where A2 caught the ball.

Why? Because A4 did not violate, A2 did. A4 fulfilled all of the requirements of the throw-in, so this is not a throw-in violation. This is an OOB violation by A2 per 9-3-2. The penalty for 9-3-2 is a throw-in to the opponent from the nearest spot of the violation. That is where A2 touched the ball.

(What Nevadaref said)

Plus the conceptual "why"....

Image if the pass was, instead, caught/touched by B2 at that spot. Who's ball would/should it be? Would it make sense to consider it a violation on the thrower and give the ball to B? If it were that way, B would only need to make sure they had a foot OOB and touch the ball on a throwin in order to be awarded the ball rather than actually intercepting/stealing it. Of course, it would only occur on a throwin near the sideline/endline but it could occur.