[Skahtboi]

ASA reads:

Before starting the delivery:

(Male only) The pitcher shall take a position with his pivot foot in contact with the pitcher's plate and his non-pivot foot on or behind the pitcher's plate.

(Female only) The pitcher shall take a position with both feet in contact with the pitcher's plate.

Note that this is prior to delivery. Don't confuse it with what the pitcher can do in delivering the pitch. Here is what ASA says about that.

In the act of delivering the ball, the pitcher must take one step with the non-pivot foot simultaneous with the release of the ball. The step must be forward and toward the batter within the 24-inch length of the pitcher's plate. It is not a step if the pitcher slides the pivot foot across the pitcher's plate toward the batter, or if the pivot foot turns and slides in order to push off the pitcher's plate, provided contact is remained with the plate.

(Women's and all JO play.)Pushing off and dragging the pivot foot in contact with the ground is required. If a hole has been created, the pivot foot may drag no higher than the level plane of the ground.

(Men only)Pushing off and dragging the pivot foot in contact with the ground, or if both feet are in the air, having the toes of the pivot foot in a downward direction is required.

Most rules in the various sanctioning bodies are similar to this, though I am not sure about BR or LL. NFHS and USSSA allow female pitchers to start with the non-pivot foot in contact with the pitcher's plate or behind it.