handShotgun can no longer be called once someone’s hand is holding the Shotgun door handle. This officially stakes their claim to Shotgun and calling it at this time is simply redundant.

This is one scenario where a person does not actually have to say Shotgun to get the seat. The importance of this rule is that no one has to be around for you to stake your claim to Shotgun, whereas usually one other would-be occupant would have to be present for you to call it.