In football, an signal is when the QB, just before the start of the play, changes the pre-determined play at the line of scrimmage. Essentially, it's a sudden adjustment! The QB might notice something on the defense https://xem-bng-trc-tip-ko-nh-ci746282.tusblogos.com/42807485/the-is-an-play-call-in-football-an-easy-explanation