The rules concerning the forward pass between 1906 and 1914 were quite different from today. At the time, the forward pass was an experiment to make the game safer. None of the rule makers of 1906 knew whether it would work or how they might need to tweak the rules to make the forward pass successful.
Initially, passes had to be thrown from a spot five or more yards to the right or left of the center, and passes thrown over the goal line touchbacks. A rule switch in 1910 required throwing the ball from five yards behind the line of scrimmage, a rule the colleges retained until 1946. The same year, passes traveling more than twenty yards downfield became illegal, a rule cast aside two years later.
While those rules are worthy of separate articles, the current focus is on incomplete passes. Among the original restrictions on the forward pass was a rule that passes hitting the ground without touching a player on either side resulted in a turnover, with the opponent taking possession at the spot of the pass. In 1907, they changed the penalty from a turnover to a 15-yard penalty and further specified that the rule applied only when the ball landed in the field of play. A new rule covered forward passes landing out of bounds, in which case, the ball belonged to the opponent where the pass crossed the sideline. The combination of rules made the forward pass risky, so many teams were reluctant to use it, mainly because few players knew how to throw the ball well, and fewer coaches knew how to design plays to take advantage of the forward pass.