Sandbag

[Donald Trump]

When a player in any game chooses (on purpose) to not play their best. Normally this is because they are too superior, they want to hustle you, or they are too lazy to play their best with nothing on the line.
Also see [sandbagging] (verb form)

[Rihanna]

someone who slows you down either by their pure retardedness or by their unwillingness to cooperate.

[Jason Yan]

A bag filled with sand, typically used for defensive purposes or as ballast in a boat.