Had this last night in a 7th grade boys A-Team game.

A1 is at the free throw line for a 1 an 1 shot. B1 is behind the 3-point line. B1 take a running start and tries to time the ball hitting the rim before he crosses the 3-point line for the rebound.

Question: Can B1 take a running start or does he have to stay in a spot until the ball hits the rim.

What the call?

In this game he crossed the 3-point line before the ball hit the rim. Tweet! Line Violation!

B1 can take a running start. He can even do the shimmy-shimmy-shake and do some jumping jacks on the way. The rule is just that he can't cross the 3-pt. line prior to the ball hitting the rim or backboard.

Z

Also, a player may not cross the foul line extended before the ball strikes iron.

or backboard

Z

Did you mean the top of the key extended
 

I thought they had to stay behind the top of the key extended until it hits the goal. The shooter has to stay behind the free throw line.

Players can go as far as the FT line extended behind the 3pt line, before the ball hits the rim.

9-1-8 ... A player, other than the free thrower, who does not occupy a marked lane space, may not have either foot beyond the vertical plane of the free-throw line extended and the three-point line which is farther from the basket.

While not clearly written (I don't get the part about farther from the basket.), it means that you must be outside the three point line and behind the free throw line extended. Also notice that strictly speaking you can't break the plane with your foot in the air, which is tougher than just not touching the floor inside before the ball makes contact. Otherwise the player may move around freely out there.
Similar to the players who are not jumpers and do not take a position on the restraining circle for the jump ball. Many people think that they have to be stationary. They may run around if they wish.

Nevada,

Yeah, that IS poorly written. I think what they meant to convey was "...the 3-point line, whichEVER is farther from the basket."