Balk Move?

I'm going to say 'not a balk' because there's no rule that specifically prohibits it.

I would say not a balk simply because he threw the ball.  The rule specifically says that he cannot feint a throw to 1B while engaged with the pitcher's plate.  He threw the ball.  No balk.

That's a balk on two counts:

1) He failed to pitch to the batter when the entire non-pivot foot passed behind the perpendicular plane of the back edge of the pitchers plate.  (The only exception is on throws to second base.)

2) He didn't step directly toward the base he was throwing to.

Here is why I say it isn't a balk.  I re-read Section 1, Art 3 which says, "[n]atural preliminary motions such as only one stretch may be made. During these preliminary motions and during the set position until a delivery motion occurs, the pitcher may turn on his pivot foot or lift it in a jump turn to step with the non-pivot foot toward a base while throwing or feinting as outlined in 6-2-4 and 2-28-5."  Because he made a jump turn, granted in a 270 degree movement, it is not a balk just the same as a jump turn 90 degrees isn't a balk.

Bill: 

The authorization to make a jump move doesn't make all jump moves legal or give give immunity from the list of balk moves:

6-2-4b: Failing to step with the pivot foot directly toward a base when throwing or feinting there in an attempt to put out or drive back a runner.

There is no way that a 270-degree turn can be construed as stepping directly toward a base. 

6-2-4f: Failing to pitch when the entire non-pivot foot passes behind the perpendicular plane of the back edge of the pitcher's plate, except when feinting or throwing to second base in an attempt to put out a runner.

This rule outlaws 270-degree turns to either first or third. Runners on corner bases are entitled to know that the non-pivot foot going behind the rubber means that the pitcher is throwing home.

This is a no-doubter balk on both counts. There's a reason you don't see this move very often. That's because it's illegal.