The final, and arguably most critical innovation, which might finally make American football uniquely "American", was the legalization of interference, or blocking, a tactic which was remarkably illegal beneath the rugby-style principles. Interference continues to be strictly illegal in both equally rugby codes. The prohibition of interference in the rugby match stems from the sport's stringent enforcement of its offside rule, which prohibited any participant over the group with possession with the ball to loiter between the ball along with the intention. Initially, American gamers would obtain Inventive means of aiding the runner by pretending to unintentionally knock into defenders trying to tackle the runner.

The most common "subs" are likely with a few source defensive linemen and 4 linebackers, but retaining the secondary (the cornerbacks and safeties) exactly the same.