Legal Slow Softball Pitch

Question
This last Thursday, I was called for an illegal pitch by an umpire on a pitch i've been using for three years now with no previous problems.  I start with both feet on the rubber, and throw the pitch normally, with the only difference being I step to the right, instead of forward.  I do not hide the ball, stop/reverse my motion, or throw it behind my back.  The umpire informed me that I had to make a motion to the plate.  There is no stealing in my league, so I do not see the problem.  Please help

Answer
Good morning Douglas,
The step can be forward, backward or to the side provided the pivot foot is in contact with the pitcher's plate and the step is simultaneous with the release of the ball.

So everything else on the pitch being legal the umpire was incorrect in calling an illegal pitch on you.  I have no idea what "make a motion to the plate" means.

Hope this helps
Mark