For those that are interested, here is somebody's break down of a Cover-3 Defense, complete with definitions, still pictures, diagrams, and plenty of links to further information: Jaguars Film Room: Coverage with the Cover-3 - Big Cat Country Coverage Zone Rules Now that we know how the defense numbers the receivers' distribution before the snap, the next step is learning the actual rules of pattern-reading. Remember, the pass defenders aren't just dropping to an area and breaking on the ball, they're looking to take away specific things, starting with vertical threats up the seam (the biggest potential void in the defense). Courtesy of Shakin the Southland: Flat - Stays inside the alignment of #1 receiver to that side but stays outside everyone else, so any receiver that comes toward the sideline must not get wider than the flat defender is playing. As we defined before, it means he can't let anyone cross his face without breaking on the route. His aiming point in his drop is 10 yards deep in the seam and anyone that comes nearby should be rerouted by force. The man playing the flat or curl/flat area is generally the guy with the toughest assignment because of the amount of yards he must cover. Hook/Curl - Original drop inside the #2/3 receiver, and must never let someone go up the seam undefended. Based on the release of the #2 receiver, he stays on the inside edge of the numbers. If he's on a TE, he must get his hand on him. Exactly what he does to him depends on whether the TE starts outside or inside from the LOS. If he goes outside, the defender drops 10 yards and immediately looks for a Smash pattern. Deep Coverage - Corners take anyone man/man who goes deeper than 12 yards from the LOS, while the middle coverage defender (FS/SS) watches the seams to either side. These rules are pretty universal against almost any pass concept the defense can see. As such, it's easy for sub package players, such as a nickelback or a third safety, to come in and execute the exact same coverage responsibilities as the man he replaced. Just remember that the underneath defenders priorities go (in order): 1. Re-route any vertical threat to protect the seams and then 2. Read for a corresponding in our out break depending on their relation and leverage to the receivers post-snap.