Checkdowns are not called from the sideline. They are snap decisions by the QB when his first and second options are not available, or where there's a rush overload and he has to throw hot. Neither are play changes called from the sideline; all in-helmet speakers are shut off by the NFL with 15 seconds left on the playclock. At that point all decisions are in the hands of the QB. A designed throw behind the LOS can easily be seen by what the other players on that side of the QB are doing. Screens & bubble screens and the like require virtually _all_ the players on that side to be participating in the play, because there are so many defenders around that they all need to be blocked. Screens are most vulnerable to backside pursuit, so the strongest signal is how the line or TEs are handling defensive linemen - are they blocking them towards the QB (i.e. screen) or towards the outside (i.e. not a screen). Also the offensive pass interference rules require the blocking on bubble screens to happen at a precise time, otherwise the blockers will get flagged if the ball is not yet in the hands of the receiver. So if you have a couple of guys running out or up, and then a throw to a back behind them, it is almost certainly a checkdown instead of a designed play. From what I could see, most of the dumpoffs weren't designed plays, they were checkdowns. Which is what makes this premise about Chan Gailey so funny. Fitzpatrick is clearly a short thrower at this point of his career. Long throws to stretch out the field aren't working. The defense is flooding the short zones forcing Fitz to throw checkdown after checkdown. So why not _design_ more plays for short throws? The offensive playbook doesn't particularly seem more creative.
