Matt Waldman’s RSP NFL Scouting Glossary with the help of Florida Gators NFL Draft prospect, Justin Shorter, illustrates the concept and technique of framing horizontal space on a vertical route. 

What Is Framing Horizontal Space/Measuring the Opponent?

To the uninitiated, this move looks like a push-off during the receiver's break on a vertical route. If not executed correctly, it becomes a push-off and offensive interference. It makes this a controversial topic among fans, media, and even some defensive back coaches, but it's a legitimate move that NFL receivers lean on, week in and week out.

Framing Horizontal Space, or Measuring the Opponent, is the extension of the arm toward the defender next to him with the purpose of reinforcing the existing space that's already between them. The receiver only delivers resistance with that arm if the defender leans into the receiver's hand after the arm is already extended.

The purpose is to maintain the horizontal space between the receiver and the coverage so the defender can't get into the receiver's frame and attack the target. This technique is usually performed during the break of a vertical route, especially near the boundary.

The reason I also call it "Measuring the Opponent," comes from boxing. Fighters frequently extend their arms into opponents without delivering a punch. They may make contact with their opponents when they do this, but they aren't delivering forceful contact.

The purpose is essentially the same as it is for wide receivers: Reinforcing the space that's already there as a way of setting up their next move that requires the established distance between the two combatants. Boxers call this technique Measuring the Opponent.

Why Is Framing Horizontal Space/Measuring the Opponent Valuable?

Outside receivers are encouraged to run vertical routes so they have enough space between the numbers and the sideline. This gives the quarterback enough room to make an accurate throw. This space also allows the receiver to make a late fade toward the boundary, which creates additional horizontal separation between himself and the coverage.

This is often known as "buying back the boundary." It's a valuable technique because it allows the quarterback to target a receiver even when there's little if any vertical separation between the receiver and the defensive back. This horizontal space between the receiver and the boundary is the leverage advantage that quarterbacks with strong processors see when they decide to pull the trigger.

Framing Horizontal Space reinforces that space and when done correctly, officials see it as the receiver owning the space he has already earned. If the defender leans into that space, the receiver can give resistance to defend the space he already has. If his resistance becomes too forceful, it crosses the line from defending space to creating additional space through the aggressive actions of a push-off.

When a defensive back is tight to a receiver on a vertical route, whether he's side by side with the receiver or tight to the back or front hip, the defender will try to close the gap between himself and the receiver so he can play the ball. He's trying to earn a position where he can run the receiver's route and win the ball. This happens after the break and during the final stages of the target's trajectory.

Framing the Horizontal Space is the receiver's preemptive act of preventing the defender from closing the gap. If he extends his arm away from his frame before the defender closes the gap, then it's the receiver claiming the space. If the defender leans into it, it's no different than if the receiver wasn't giving up ground if the defender was leaning into the receiver's body because the receiver already established that space as his.

This is what officials see and why not everything people think is a push-off is actually a push-off. Again, if the receiver moves the defender with his extended arm after the de...