I found this ditty from a 1960s Sports Illustrated interview with Fritz Crisler, and wow, this is classic:
In a moment [Crisler] went on: “I remember the old plays. The hurry-up huddle, the sideline and talking plays. The sleeper.” He smiled. “Our defense against the sleeper was rather celebrated. The sleeper was banned by the Rules Committee, but when the play was legal a man could hide out over where there were substitutes standing or where there was a crowd on the sidelines. You would tell your halfbacks, ‘Scan your sides of the field after every play to look for that sleeper.