1.A player that succeeds in playing so fantastically bad that it is considered a form of art.
2.Someone who is incapable of competing effectively when the situation calls for it.
3.A player who makes a career of faltering in the clutch situation.
Tony Romo is the complete choke artist. He has great stats during the regular season, but then he just chokes so hard in the playoffs.
Also see; Donovan Mcnabb, Kobe Bryant(without Shaq), Alex Rodriguez, Terrell Owens, and the Buffalo Bills of the early 90's