The person who is currently in the last qualifying position at a pinball tournament (for example: 16th place out of 16 qualifiers). The Gatekeeper must be sure to rigorously defend the position or work quickly to move higher in the standings.
The Gatekeeper is the one who is mostly in danger of being kicked out of the playoffs by the people below. He may choose to play Defense against one or a few players who are ranked behind him.
The Gatekeeper must also watch out for snipers who are looking to jump him in the standings, especially the Bubble Boy.