second guesser

Etymology
From.

Noun

 * 1) A person who second guesses.
 * 2) * 1988 October, George Vass, “World Series: A Magnet for the Second-Guessers”, in Baseball Digest, volume 47, number 10, Lakeside Publishing Company, ISSN 0005-609X, page 21:
 * Such a change of heart in MacPhail, or any other second guesser, is unlikely.