http://www.nfhs.org/Sports/basketball_emphasis.htm
3. Free Throw Administration
Over the years, the rules committee has been concerned with the increase in rough play during free throws. There have been many rules changes and Points of Emphasis in recent years to address these concerns. In 1997, the committee returned to the restrictions on lane-line players to be in effect until the ball hit the rim or backboard. This change has greatly reduced rough play. In an attempt to further reduce rough play and have the defense regain some of the advantage they may have lost when the rim restriction was reinstated, the number of players permitted in the marked lane spaces has been reduced. In addition to this years rule change, the following items are to be emphasized during free throws:
A. Lane-Space Requirements: The first two lane spaces adjacent to the end line must be occupied by the opponents of the free thrower. If the offense desires the second spaces, they may have them. If the defense desires the third spaces, they may have them. If a player entitled to the second or third space does not occupy that space, an opponent may be in the space (within the number limitations, four defense and two offense). The fourth marked lane spaces (nearest the free-throw shooter) may not be occupied. All officials are responsible for ensuring players are in their proper spaces. The administering official (Lead) should check each space for proper alignment before bouncing the ball to the shooter. If these requirements are not met, see 9-1-9 Penalty.
B. Double Violation: If the offense is erroneously permitted to occupy the first two lane spaces and the defense is erroneously permitted to occupy the second two lane spaces, a double violation shall be called (9-1-2 Pen 3).
C. Disconcertion: Disconcerting the free-throw shooter is a violation (9-1-5). Officials should pay particular attention to situations in which the free throw will become dead (first of two or first two of three). Defensive players frequently employ tactics which serve no other purpose than to disconcert the shooter (instructing players to box out, waving arms, etc.). With the spaces closest to the shooter remaining vacant, disconcertion should be minimized.