No you cannot foul the inbounder. In the NBA, (Rule No. 12, Section II Article 5) a delay-of-game shall be called for a defender crossing the boundary line prior to the ball being released on a throw-in. EXCEPTION (5): In the last two minutes of the fourth period and/or overtime period, a technical will be assessed if the defender crosses or breaks the plane of the boundary line when an offensive player is in a position to inbound and prior to the ball being released on a throw-in.

In high school and college you can give a warning to reaching across the plane, on the second infraction it is a technical foul.

Since Sacredhoops.com continues to have numerous high school basketball rules (by the way keep them coming) we have partnered with a basketball referee guru. Please welcome Michael Borgelt who will be continuing to answer all your high school basketball rules, or any other basketball rule questions you might have.