Balk with No Runners on Base?

 
There is no one on base, but the pitcher is positioned in a legal set position. However, the pitcher is making no effort to come to a "complete and disenable stop" as he goes from his initial position on the rubber to delivering the pitch. The offensive coach wants the plate umpire to call a "balk", since the pitcher is not coming set (as required in NF 6-1-3). Meanwhile, the defensive pitching coach remembers Mariano Rivera pitching from the set position and never coming set when the bases were empty. What does the umpire do now?
 
Call
In NFHS, when pitching from the set position, a "complete and discernible stop" is required -- with or without runners. In the NCAA and MLB, when the bases are empty, the pitcher is not required to stop. In the situation below, when playing under NFHS rules, the pitcher has made an illegal pitch. "Time" is immediately called and a ball is awarded to the batter.