RULE NO. 9—FREE THROWS AND PENALTIES

Section I—Positions and Violations

d. During a free throw attempt for a common foul, each of the spaces nearest the end-line must be occupied by an opponent of the free throw shooter. Teammates of the free throw shooter must occupy the next adjacent spaces on each side. Only one of the third spaces may be occupied by an opponent of the free throw shooter. It is not mandatory that either of the third spaces be occupied by an opponent but may not be occupied by a teammate. If there is a discrepancy, teammates of the free throw shooter will occupy the spaces first.

I've seen this mis-interpreted at the higher level as well. This is very commonly mistakened with the College and High School rules.

1. Both High School and College does not reqire the shooting team to occupy the middle spot in the free throw lane.
2. The only spot that is optional for the non-shooting team at the pro level is the 3rd spot closest to the shooter.
3. Minimum of 4 and Maximum of 5 in the box, and the shooter.

Crew chief stuff!!