Here’s how the Cowboys let the Chiefs score that inexplicable TD to end the 1st half

The 56-yard touchdown the Chiefs’ Tyreek Hill scored against the Cowboys on Sunday never should’ve happened. It came on the last play of the first half, and 56 yards is far enough from the end zone that a Hail Mary shouldn’t connect more than once in a blue moon. But Dallas allowed Hill to score from distance anyway.

The full play:

It’s like a Hail Mary, except it’s not. Alex Smith threw to Hill when the receiver was fewer than 15 yards beyond the line of scrimmage. The NFL’s fastest player got running from there and picked up 43 yards after the catch to score.

I don’t consider myself an expert in defensive theory, but there’s a general principle that makes enough sense to me: You can’t just put everybody in the end zone and expect to defend against a touchdown that way. If a defense ever did that, the offense would line up 10 blockers in front of some speedy ball-carrier, and they’d all target the weakest point in the back line. They’d bulldoze in for a TD.

The Cowboys didn’t exactly do that here, but they got close. They started the play with seven defensive backs all chilling near the end zone, 50-plus yards from the line:

The Cowboys brought a three-man rush, the opposite of a blitz, and had a linebacker roving around near the line of scrimmage. That’s an extreme version of the prevent defense. Normally, there are boundary cornerbacks in the general area of the receivers, so they can get to them quickly enough when they make a catch. Not here.

Smith threw past that LB to get the ball to Hill, and that set up a numbers situation that, in theory, would be good for Dallas: seven tacklers deep against three blockers and Hill. If you’re just thinking in terms of addition and subtraction, it works.

An NFL field is 53.3 yards wide. The Cowboys had their deep men strewn all the way across it, which meant Kansas City only had to go after a couple of guys at a time to do a decent blocking job. Hill’s the most agile player in the world, and letting him have 30 yards of runway is nothing short of malpractice.

Hill started behind his blockers: tight ends Travis Kelce (87) and Demetrius Harris (84), and receiver Demarcus Robinson (14).

Dallas had five guys more or less right in front of Hill by the time he got to the 25-yard line. But it’s easy to see how those guys got knocked out of the play.

Kelce and Harris, the tight ends, both blocked one guy. Hill made Orlando Scandrick, No. 32, miss.

To the left of that picture, Robinson, the other receiver, was shoving two Cowboys out of the play. And suddenly all five of the Cowboys who were in Hill’s immediate vicinity were out of the picture, with Hill sprinting full speed ahead.

The Cowboys had linebacker Anthony Hitchens deep on the play, lined up as one of their backs. Hitchens is the guy in the top righthand corner in that cap above.

Hitchens comes for Hill at the end of the play, but he’s a linebacker, and Hill is Hill. That matchup ended exactly as everyone would expect, with Hill roaming free:

If the Cowboys were in a regular prevent defense, there’d have been a defensive back somewhere within one or two zip codes of Hill when he caught the pass. Hill is an outrageous athlete, but he wouldn’t have had all that free running ahead of time, and his teammates wouldn’t have gotten the chance to set up those ideal blocks.

The point of a prevent defense, obviously, is to prevent a deep throw into the end zone from getting caught. But if you completely neglect as much real estate as the Cowboys did on this play, you’re giving an offense way too much time to align itself to burn you another way. The Chiefs took advantage and made one of the better plays of 2017.