[SanDiegoSteve]

The pitcher is considered to be on the rubber when doing the 3rd to 1st move. He is not to be considered "disengaged" from the rubber, and is not considered a fielder for the purpose of this play.

Here is the NAPBL interpretation:

"It is legal for a right-handed pitcher to begin a pick-off move to first base by first moving his pivot foot in the direction of third base provided that he makes a legal step toward first base with his non-pivot foot before throwing there and provided that the move is continuous and without interruption. A pitcher who makes such a pick-off move is considered to be in contact with the rubber when he makes his throw to first base."

FED concurrs by the way. Case Book 6-2-4 SITUATION C. The pitcher can feint toward 3rd, turn and throw to first. If he throws the ball out of play the award is only one base, because he is not considered to have disengaged the rubber unless he first removes his pivot foot and steps backward off the rubber to be disengaged. He cannot feint to 3rd, turn and feint to first. This is a balk.