no stretch balk?

[dflynn]

13U traveling teams. Our runner on 1b, RH pitcher does not stretch. Pitchers hands together at waist, RH foot on rubber. Hands slightly move up like going into wind-up, at very same time RH foot steps back and throws to first. R1 is stealing on hand movement up as coached, but is picked off by P move to first. R1 is out in run-down. No balk is called. Umpires say pitchers hands moving at same time his foot comes back off rubber is part of P move to first and no balk allowed. Is this a legal move by pitcher? If so, I want to add to my play list. thanx.