It all depends on whether that is really meant to stop at the boundary line, or was meant just for lateral movement.

One interp says, " he or she may move laterally if at least one foot is kept on or over the designated area. " so that could be read as the later. But, the same interp says "jump vertically" so that could be read as NOT allowing a jump over the court.

It has been discussed here in the past, and I thought there was a defining case or interp, but I can't find it.

In spirit, I agree. But, as written, the rule defines it as an intentional foul for a defender to contact a thrower. It doesn't distinguish between who causes the contact. Just that their is contact. I think it is a stupid rule.

I think "contact" in this case is an action verb -- the defense must act to cause contact.

It does not say "or is contacted by the inbounder".

And, the relevant case play has it as either a throw-in violation or a foul on the offense -- but not as an intentional foul on the defense.

That case play predated the change to making contact with the thrower an IF...who knows if they considered it when they changed the rule for no good reason.

Even if you're right (and I think you likely are), it is still a dumb rule. If B1 can legally play the ball when it is held beyond the throwin plane, they should not , as long as the action is entirely on the inbounds side of the line, be liable for an IF if they miss the ball and hit the throwers arm instead. There is nothing about that play that needs to be an IF.

Reaching through the line and fouling the thrower being ruled and IF, as has always been the case, was sufficient.

I agree with that.