You've seen this scene play out thousands of times: While the play clock is winding down, the quarterback reads the defense and adjusts the play, protection and routes at the line of scrimmage, sometimes until the final milliseconds before the officials call him for delay of game. A blitz comes, and the quarterback, if he is worth his salt, will get the ball to a receiver before a pass rusher is all over him.

"The quarterback is not going to hold the ball," Vikings defensive line coach Andre Patterson said.

That's the football you're accustomed to, but it's a scenario happening less often in recent years.

In the unceasing cat-and-mouse game between offenses and defenses, teams are blitzing less. On top of that, teams are having more success with only sending four pass rushers.

The NFL has morphed into a passing league — and defenses have figured out the best way to combat that is with fewer blitzes. While it would appear that strategy defies logic applied for decades, there's proof that it's working.

Get this: NFL teams had a total of 641 sacks in 2015 when sending only four rushers an average of 25.1 times per game. The number of sacks jumped to 736 in 2017 with teams sending four rushers an average of 24.5 times per game, according to the sports data firm Sportradar.

At a recent Vikings practice, coaches and players offered some theories as to why teams are better at sacking the quarterback utilizing only four pass rushers.

To Patterson, the reason is simple — teams are opting to drop players in coverage more often in an effort to make quarterbacks go through their progressions. That forces them to hold on to the ball longer and results in more sacks for the four pass rushers.

"When you show pressure, the ball is [quickly] coming out," Patterson said. "When you show coverage, now the quarterback is more likely to go from his first read, to second read, to third read. That's why the numbers are greater on a four-man rush, because the quarterback is going more through his progression [than] if it was a five- or six-man pressure."

In 2017, teams sent five pass rushers, or one blitzer, an average of 7.2 times per game, resulting in 297 sacks. That's down from 8.5 times per game (335 sacks) in 2015.

The numbers on six-man pressure have also gone down, from 2.5 times per game in 2015 to 2.0 in 2017.

Vikings coach Mike Zimmer said some of the defense's success in backing off the blitz might have to do with the experience of offensive linemen coming from college spread offenses into the NFL, where they aren't necessarily prepared for the pass rushes they see.

"They're used to slide protections in college," Zimmer said. "A lot of this stuff that we do is a lot different."

In spread offenses, quarterbacks get the ball out quick, which alleviates pressure on the offensive linemen, but in the NFL, offensive linemen might have to hold blocks longer. Blitzing, and forcing the quarterback to release the ball early, can play into the offensive linemen's hands. But making the quarterback hold the ball forces linemen to hold their blocks longer — something younger linemen might not be accustomed to doing. Patterson didn't buy the spread-offense theory, at least when it comes to a team's starting five when all are healthy.

But Vikings defensive lineman Stephen Weatherly said his position group could have a leg up on those types of linemen in their first years in the league.

"If you're not used to holding a block for four, five seconds and you're used to quick hot routes, that can be a really big jump," Weatherly said. "You're used to stopping a guy's first move and the ball is out. What are you going to do when he converts to power, spins off of that or something like that … especially when you have someone like [defensive end] Everson Griffen bearing down at you who has a second and third move in his holster ready to use?"

Sportradar's tracking data for this specific statistic goes back only to 2015. In 2016, the numbers began moving toward where they would eventually be in 2017 — with five pass rushers coming on 7.7 plays per game and sacks with four rushers increasing to 703.

The Vikings in 2017 sent an extra rusher on about seven plays per game and got 27 sacks when rushing only four. That ranked ninth in the league. In 2015, the Vikings sent a fifth rusher about nine times per game, so they fell in line with the trends of the league.

"I'd think probably there's a lot of elements that go into any quarterback sack," Vikings co-offensive line coach Clancy Barone said. "That's true every year, that's not just new in 2017 or new in 2015. That's the same every year. It's all 11 guys being on the same page, knowing when they're hot, when they're not."

Of course, teams still try to disguise where the pass rushers might come — they might not always be four linemen or linebackers. But the numbers game suggests teams more routinely now only want to send four regardless of their position on the field.

Offenses have incorporated more chip blocks from backs and tight ends, who then go out to catch passes as one counter, Patterson said.

"You'll see teams that put the tight end in a wide off position, have him chip the end on the way out on one side and have the running back chip the end on the other side on the way out," Patterson said. "We got a lot of that because people respect our rushers."

Patterson added that when you bring extra rushers, the QB "always has an outlet to get the ball out of his hands."

Teams don't want to give the quarterback an outlet. They'd rather make him sift through coverage and hopefully put him on the ground.

Chris Hine is the lead writer for North Score, the Star Tribune's sports analytics beat. startribune.com/northscore E-mail: chris.hine@startribune.com

Ben Goessling contributed to this report