Balk Justification

[Rufus]

OBR rules. R2, less than two outs, pitcher comes set and begins delivery to the batter. As he's pushing off his pivot foot, his hands separate and then he experiences extreme pain in the pivot leg (popped hamstring, cramp, etc.). This causes him to stop the delivery motion, grab the leg with his pitching arm (ball still in hand), and fall off the mound.

This happened during the Braves/KC game Monday and the umpires called a balk, awarding one base to R2. My questions:

• Is the balk called because of 8.05(a)? If there is a runner, or runners, it is a balk when-the pitcher, while touching his plate, makes any motion naturally associated with his pitch and fails to make such a delivery
• Since this is a balk the ball is dead by 5.09(c), correct?

Thanks in advance.