The final, and arguably most significant innovation, which might at last make American football uniquely "American", was the legalization of interference, or blocking, a tactic which was hugely unlawful beneath the rugby-design and style principles. Interference continues to be strictly illegal in equally rugby codes. The prohibition of interference in the rugby recreation stems from the sport's strict enforcement of its offside rule, which prohibited any player over the group with possession on the ball to loiter between the ball as well as site the target. Initially, American gamers would obtain Inventive ways of aiding the runner by pretending to unintentionally knock into defenders trying to tackle the runner.

The original four-group league expanded to sixteen teams in 1933 when Pop Warner, who had just been hired as the new coach in the Temple University football crew, agreed to offer a lecture on the boys from the league. In his honor, the league was renamed the Pop Warner Meeting.[209][210]