A lame duck, in the context of a game

Game

A game is structured playing, usually undertaken for enjoyment and sometimes used as an educational tool. Games are distinct from work, which is usually carried out for remuneration, and from art, which is more often an expression of aesthetic or ideological elements...

, is a player who remains in the game but has no chance of winning. It must be literally impossible— not merely highly improbable — for a player to win for it to constitute a lame-duck scenario. If a game frequently admits lame-duck scenarios, this is considered a severe design flaw.

A kingmaker

Kingmaker scenario

A kingmaker scenario, in a game of three or more players, is an endgame situation where a player unable to win has the capacity to determine which player among others is the winner. Said player is referred to as the kingmaker or spoiler...

is a lame duck who retains the ability to select who, among other players, will win the game.