Monday morning quarterback
A person who acts like they have all the answers to a problem, especially in hindsight, usually without having any experience in that area. Likened to fans and commentators who criticize a football team after a Sunday game. Primarily heard in US. Social media seems to have turned everyone into a Monday morning quarterback whenever political issues are discussed.
A person who criticizes or passes judgment from a position of hindsight, as in Ethel was a Monday-morning quarterback about all the personnel changes in her department-she always claimed to have known what was going to happen . This expression, first recorded in 1932, alludes to fans who verbally "replay" Sunday's football game the next day, the quarterback being the team member who calls the plays.
See also: quarterback