Balk Definition: What Constitutes an Illegal Pitch?

Question
Good day,
is it a balk when:
runners on base
pitchers hat falls off when delivering a pitch to batter
thank you

Answer
Rich,

I would interpret this as not a balk.  It is a balk if the pitcher drops the ball, but there is nothing in the rules about a piece of the uniform coming off while pitching.

If it happened on every pitch though, I might have to make some kind of umpire judgement...

Hope this helps!

Brian