A route run by a receiver in football that requires the receiver to run straight upfield toward the end zone. The primary goal is to use fast, vertical speed that puts the receiver behind any defensive backs attempting to defend the play.
The fly route (also known as the “go” or “streak” route) is usually reserved for wide receivers on an offense with the best combination of physical speed, strength and awareness. Because of this athleticism, players who can consistently run the fly route can usually run any route well. Receivers running a fly route must sprint toward the end zone and turn or fight back to receive the pass. The quarterback should only have to throw behind the defender to complete a pass to a receiver on the fly route, although a lot depends on the ability of the receiver to keep an advantage over his man.
The fly route is not incredibly efficient—it typically has a low completion percentage and defenses are often designed to take away big plays by limiting the deep field. But even with these considerations, go routes can do a lot to open up a defense. Teams will often run fly routes in an attempt to keep defenses honest, expanding the rest of the field for other patterns to find completions.