College football began its modern period in the 1940s, when the game took on basic qualities that it retains fifty years later. College football was revolutionized by one major rule change — the free-substitution rule — and one major tactical innovation — the refinement of the T-formation to exploit the passing game that stimulated a flood of lesser rule changes.

Free Substitution.

The free-substitution rule, which went into effect in 1941, had repercussions far beyond those intended. Before the war eleven men on a football team played the entire game, offense and defense. Only injury was grounds for substituting. The new rule allowed players to substitute for one another at any time, except during the last two minutes of the first half. During the war free substitution was the salvation of college football, allowing weakened teams to continue playing. When the war was over and...