High school fake to 3rd play

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can someone explain how someone can fake to 3rd and throw to first without disengaging? In my case i was trying to describe the pitcher stepped to 3rd with his left ft, followed thru and his right foot came off ending up parallel with his left, he then turned and threw to first.

could he fake a throw to 3rd without stepping with an arm fake and then reverse and throw to first? if so he doesnt need to step back off the rubber?

or is there some other way to fake the throw and not disengage?