the quarterback became the primary "blocking back", leading the way through the defense but rarely carrying the ball themselves. This was the primary strategy of the single wing offense which was popular during the early decades of the 20th century. After the growth of the forward pass, the role of the quarterback changed again. The quarterback would later be returned to his role as the primary receiver of the snap after the advent of the T-formation offense, especially under the success of former single wing tailback, and later T-formation quarterback, Sammy Baugh. The requirement to stay behind the line of scrimmage was soon rescinded, but it was later reimposed in six-man football. The exchange between the person snapping the ball (typically the center) and the quarterback was initially an awkward one because it involved a kick. At first, centers gave the ball a small boot, and then picked it up and handed it to the quarterback. By 1889, Yale center Bert Hanson was bouncing the ball on the ground to the quarterback between his legs. The following year, a rule change officially made snapping the ball using the hands between the legs legal. Several years later, Amos Alonzo Stagg at the University of Chicago invented the lift-up snap: the center passed the ball off the ground and between his legs to a standing quarterback. A similar set of changes were later adopted in Canadian football as part of the Burnside rules, a set of rules proposed by John Meldrum "Thrift" Burnside, the captain of the University of Toronto's football team. The change from a scrummage to a "scrimmage" made it easier for teams to decide what plays they would run before the snap. At first, the captains of college teams were put in charge of play calling, indicating with shouted codes which players would run with the ball and how the men on the line were supposed to block. Yale later used visual signals, including adjustments of the captain's knit hat, to call plays. Centers could also signal plays based on the alignment of the ball before the snap. In 1888, however, Princeton University began to have its quarterback call plays using number signals. That system caught on and quarterbacks began to act as directors and organizers of offensive play. Early on, quarterbacks were used in a variety of formations. Harvard's team put seven men on the line of scrimmage,