The King's Prerogative is a rule allowing for a king to fight their way out of a checkmate position by facing multiple opponents simultaneously. This was most famously implemented by David P. Schneider in the 2014 Championship.
The starting position for a king's prerogative must involve a king in checkmate, but able to attack one of the pieces directly threatening their space. The piece they are able to attack must be supported by another piece (thus preventing the king from entering a threatened square and making it a genuine checkmate).
Example: provided is the position known as "scholar's mate" in tabletop chess. The black king is threatened by the white queen, and cannot move to a safe space (their only move would be to a threatened square) nor can they interpose another piece to break the check (the two pieces are adjacent). No piece is able to capture the threatening piece (the queen, in this case.) Under standard chess rules, the black king would not be allowed to capture the white queen, because doing so would put them in a square threatened by the white bishop. Under King's prerogative, the black king moves to capture the white queen, and then fights a 2-on-1 bout against the white queen and the supporting bishop simultaneously.
Bout Rules Edit
In a King's Prerogative match, the king must defeat both competitors per standard victory conditions. Should either of the opposing pieces defeat the king, the game is over (as though it were a king in single combat.) As soon as one of the attacking pieces is defeated, the Marshal calls a hold to remove that competitor from the board, but keeps their weapon where it was last (frequently leaving it on the board where they were defeated).
If the attempted King's Prerogative is successful, the king moves to capture the directly threatening piece (where the white queen was in the example) and both of the threatening pieces are removed from the board. The play continues with the turn of the formerly checkmating side, as calling king's prerogative counts as the turn for the checkmated king.