also: dagger concept
A deep route run to clear a safety out, with a dig route coming in behind it into the space he left. A concept built to attack the middle of the field on second reaction.
An inside receiver runs a vertical route up the seam, and another receiver runs a dig, an in-breaking route around fifteen yards, behind him. The seam route's job is not to catch the ball: it is to carry the deep middle defender away, and the dig arrives in the space he vacated.
What separates it from most concepts is that the clearing route and the target are on different timings on purpose. The quarterback is not reading two routes against one defender at the same instant; he is waiting for the deep defender to declare, and then throwing behind him. That makes it a slower concept than a high-low and a harder one to run against pressure.
It is aimed at single-high coverage, where there is one deep middle defender to be moved. Against two-high there is nobody to clear out and the concept has to become something else.
dagger conceptsmash, floodDagger is the clearest common example of a route run to be ignored. A receiver whose route exists only to move a defender is a normal and important thing in a passing game. It is worth telling a young receiver explicitly, because the ones who do not know it stop running the route hard.
Demands more from a quarterback than a high-low does, because the throw is late by design and goes into the middle of the field, which is where the worst outcomes live.