Clark Daniel Shaughnessy (originally O'Shaughnessy) (March 6, 1892 – May 15, 1970) was an American football coach and innovator. He is sometimes called the "father of the T formation" and the original founder of the forward pass, although that system had previously been used as early as the 1880s. Shaughnessy did, however, modernize the obsolescent T formation to make it once again relevant in the sport, particularly for the quarterback and the receiver positions. He employed his innovations most famously on offense, but on the defensive side of the ball as well, and he earned a reputation as a ceaseless experimenter.
Shaughnessy held head coaching positions at Tulane University, Loyola University New Orleans, the University of Chicago, Stanford University, the University of Maryland, the University of Pittsburgh, the University of Hawaii, and in the National Football League with the Los Angeles Rams. Shaughnessy also served in advisory capacities with the Chicago Bears and the Washington Redskins.
He reached the height of his success in 1940, in his first season at Stanford, where he led the Indians to an undefeated season that culminated with a Rose Bowl victory. That year, he also helped prepare the Chicago Bears for the 1940 NFL Championship Game, in which they routed Washington, 73–0. Shaughnessy's successes showcased the effectiveness of the T formation and encouraged its widespread adoption. He was inducted into the College Football Hall of Fame in 1968. Shaughnessy also coached college basketball at Tulane University. He played college football at the University of Minnesota.