bounds, the center had to snap the ball from the sideline, an awkward place to start a play. Despite these constraints, player-coach Curly Lambeau of the Green Bay Packers, along with several other NFL figures of his era, was a consistent proponent of the forward pass. The Packers found success in the 1920s and 1930s using variations on the single-wing that emphasized the passing game. Packers quarterback Red Dunn and New York Giants and Brooklyn Dodgers quarterback Benny Friedman were the leading passers of their era, but passing remained a relative rarity among other teams; between 1920 and 1932, there were three times as many running plays as there were passing plays. Early NFL quarterbacks typically were responsible for calling the team's offensive plays with signals before the snap. The use of the huddle to call plays originated with Stagg in 1896, but only began to be used regularly in college games in 1921. In the NFL, players were typically assigned numbers, as were the gaps between offensive linemen. One player, usually the quarterback, would call signals indicating which player was to run the ball and which gap he would run toward. Playcalling (or any other kind of coaching from the sidelines) was not permitted during this period, leaving the quarterback to devise the offensive strategy (often, the quarterback doubled as head coach during this era). Substitutions were limited and quarterbacks often played on both offense and defense. The period between 1933 and 1945 was marked by numerous changes for the quarterback position. The rule requiring a quarterback/tailback to be five yards behind the line of scrimmage to pass was abolished, and hash marks were added to the field that established a limited zone between which the ball was placed before snaps, making offensive formations more flexible. Additionally, incomplete passes in the end zone were no longer counted as turnovers and touchbacks. The single-wing continued to be in wide use throughout this, and a number of forward-passing tailbacks became stars, including Sammy Baugh of the Washington Redskins. In 1939, University of Chicago head football coach Clark Shaughnessy made modifications to the T-formation, a formation that put the quarterback behind the center and had him receive the snap directly. Shaughnessy altered the formation by having the linemen be spaced further apart, and he began having players go in motion behind the line of scrimmage before the snap to confuse defenses. These