ChessVariant:

Regarding Pawns in the variant Protected Chess, I gave it some thought, but couldn't come up with anything that I thought was logical and playable and consistent with the other promotional piece abilities.

For instance, one thought I had was....

Pawn: Moves, captures, and promotes like a Pawn if unprotected.  Moves (straight ahead) but can't capture (diagonally) or promote if protected.