A key
A key is similar to a tell in poker – when the defense takes the field, they look for individual movement or some kind of offensive line shift that gives away which play will be run and to which side. A key can be anything from a hand movement to a change in an offensive lineman’s stance that telegraphs what’s coming. The one key that is, in my opinion, the hardest to control, is when a quarterback focuses on the receiver he’s going to throw to — learning not to do that is something that takes time, and the good quarterbacks know how to keep the defense guessing by never focusing on one player for more than a couple of seconds.