Before teams began huddling in the 1920s, teams warmed up with signal practice. That is, quarterbacks called out coded signals to their teams indicating the upcoming play and snap count. Teams then ran those plays against air.

As Yale and Princeton called signals before their 1909 matchup, neither team had their subs shield the opponent's view. They even let their opponent listen in. It probably didn’t matter anyway. Yale, under Howard Jones, won 17-0 to finish 10-0. Six Yalies were consensus first-team All-America, and the team would be retroactively named national champs.

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