Not adjusting to Cover 2I'm starting on this play, where there is clear miscommunication, because it provides me evidence on the next play. After the play, the tight ends points to himself, saying, "my bad," because he sat down in the hook zone rather than taking the route to the corner.
The easiest way to show why you use route adjustments is with diagrams.
Now against Cover 3, the opposite is true. The corner is no longer open because there is a cornerback sitting directly in that third. Meanwhile, because of how the coverage has rolled, sitting in the hook/curl zone will come open, as you pick on the flat defender again and work him inside/out rather than high/low.
This sight adjustment is used depending on the safeties. A single high safety (Cover 1, Cover 3) will sit, though against man the route likely will become more of an out route instead of a hitch so that the tight end can gain separation on his defender. Against two high safeties (Cover 2, Cover 4) the No. 2 receiver (second from the outside) will attack the corner. In Cover 4, because the No. 1 receiver (farthest outside) hitches, the cornerback will come up and the defense will essentially play like Cover 2.
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To read on about route adjustments, and to see how they are done correctly, follow the link to Bucky's 5th Quarter