Before every game, San Francisco running back Raheem Mostert looks at the six dates he was cut by an NFL team. Three of those came within a four-month span in 2015. The fourth came in September 2016, one day after his friends and family threw him a party for making Cleveland’s 53-man roster. The Bears added and subtracted him shortly thereafter. By the time San Francisco signed Mostert the week after Thanksgiving 2016, he was on his seventh team in 15 months.

“Not everybody can deal with that type of stress and pain and agony that I went through,” Mostert said this week. “But I just kept the faith not only in myself, but in whoever gave me the opportunity.”

That faith paid off Sunday. More than three years after signing to the 49ers practice squad, Mostert became the first NFL player to run for more than 200 yards and score four touchdowns in a playoff game. His dominant showing sent San Francisco to the Super Bowl. He set the franchise single-game postseason rushing record before the end of the third quarter, and finished with 220 yards—the second most in league playoff history behind only Eric Dickerson’s 248-yard outing in 1986. Mostert was an undrafted player who was a wide receiver until his junior year at Purdue and then was cut by six teams before registering a single NFL carry. How did he produce one of the best postseason rushing performances of all time?

“This scheme that we run, the outside zone and inside zone, it’s been working for years,” Mostert said at his postgame press conference. “Even back when Mike Shanahan was the head coach in Denver and even in Washington. The philosophy still transpires into what we run today.”

San Francisco head coach Kyle Shanahan is the son of Mike Shanahan, and the family business is turning off-the-radar running backs into stars. Mike Shanahan was the head coach of the Denver Broncos from 1995 to 2008. He won back-to-back Super Bowls with John Elway as his quarterback, and also pumped out six different 1,000-yard rushers behind a zone-running system developed by offensive line coach Alex Gibbs. Broncos running back Terrell Davis was a sixth-round pick in 1995 who opened his career with one of the best four-year stretches of all time. He logged one of just seven 2,000-yard rushing seasons in league history, was named Super Bowl XXXII MVP, and made the Hall of Fame despite playing in just 78 regular-season games.

A knee injury in 1999 changed the trajectory of Davis’s career, but the Broncos zone-running machine was just getting started. Shanahan replaced him with fourth-round rookie running back Olandis Gary, and over 12 starts Gary rushed for 96.6 yards per game, the third most in the league. In 2000, Shanahan turned to sixth-rounder Mike Anderson. As a rookie, Anderson ranked fourth in rushing yards (1,487), second in rushing touchdowns (15), and third in yards per attempt (5.0).

Two years later, Shanahan gave the job to Clinton Portis, a second-round pick out of Miami. In his first two NFL seasons, Portis rushed for 3,099 yards with 29 touchdowns while becoming the fifth player in NFL history to rush for five touchdowns in one game. But even he was replaceable. In March 2004, Denver traded Portis to Washington for cornerback Champ Bailey and replaced Portis with Reuben Droughns. That season, Portis ranked eighth in rushing yards; Droughns ranked ninth. Over the past 25 years, there have been only six times a running back drafted after the fifth round has rushed for 1,400-plus yards in a season. Five of those six came under the tutelage of Mike Shanahan.

All of this success got Shanahan’s employees poached by other teams, and the assistants spread the zone-running gospel around the league. Shanahan’s offensive coordinator in Denver, Gary Kubiak, became the Texans head coach in 2006; he hired Kyle Shanahan as his wide receivers coach and Gibbs as an assistant. Kyle was promoted to Houston’s offensive coordinator role in 2008, and in that season, third-round rookie Steve Slaton ran for 1,282 yards and nine touchdowns, ranking sixth in the league in rushing yards and tied for fifth in yards per attempt.

It doesn’t end there. Kyle Shanahan left to work for his dad in Washington. With Mike as head coach and Kyle as offensive coordinator in 2012, sixth-round running back Alfred Morris ran for a franchise-record 1,613 yards and ranked second in the league in rushing yards and rushing touchdowns (13). But the Texans didn’t suffer when Shanahan left. Kubiak hired Rick Dennison—another longtime assistant for those 1990s Broncos—to keep the zone-running scheme rolling. In 2010, the Texans struck gold again. A borderline-unknown seventh-round running back named Arian Foster led the league in both rushing yards (1,616), rushing touchdowns (16), and yards from scrimmage (2,220).

The Shanahans, and their disciples, have produced so many prolific backs because they pray at the altar of zone blocking. In this system, offensive linemen block a space instead of a person. If a defender is standing in front of a lineman’s face, the lineman blocks that guy. If not, he helps the teammate next to him, or runs in the direction of the ball and finds another defender to hit. Zone blocking is so simple that it has only two plays: inside zone and outside zone. There are thousands of nuances that can shape how those two plays work, but the essence remains the same. Longtime Browns left tackle and presumptive Hall of Famer Joe Thomas had nine offensive coordinators in his career, but his favorite was Kyle Shanahan, who held the role for Cleveland in 2014.

“My favorite offense that I have ever played in was the wide zone/Kyle Shanahan,” Thomas wrote in a Reddit Q&A in October. “I liked it the most because the run and the pass in the play-action all fit together and everything made perfect sense. It was like a computer program where everything was dichotomous; it was either a zero or a one and you knew exactly what you had to do on every single play and why, so once you memorized everything there was to know about the offense, you could turn yourself into a computer and it led to minimal amount of mistakes and you were able to make quick adjustments on the field without having to come to the sideline and ask the coach what we should do if we saw something we didn’t practice.”

If the system works and is easy for players to understand, the natural question is why everyone doesn’t do it. (Similar to other questions like, why aren’t airplanes made entirely out of black boxes? Or why don’t the Saints clone Taysom Hill?) Well, because the zone-running approach requires buy-in from an entire organization. The offensive linemen are moving a lot, so a team’s front office has to value athleticism and technique over size and strength. San Francisco’s offensive linemen this season weigh an average of 306 pounds, the lightest in the NFL, according to ESPN’s Kevin Seifert. Once the right linemen are on a roster, a coaching staff must have the patience to devote countless hours to practicing a single concept. Zone blocking is like veganism—it only works if you practice it all the time. (It’s also like veganism in that the people who love it love to talk about it.)

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Even when a line blocks perfectly, the holes created close quickly. That means running backs can’t dilly-dally in the backfield. A rusher must read plays quickly and decide where he’s going. While some running backs like Saquon Barkley or Le’Veon Bell dance and juke in the backfield, zone running asks backs to hit the hole and go upfield. For a lot of players, that approach requires unlearning years of what they’ve been taught. Playing in the zone system is as much a mental challenge as a physical one. If less-heralded running backs pick up the system, they can earn the job—even if they’ve previously been cut six times.

“You have to have vision in order to read the holes and read the gaps,” Mostert said in his postgame press conference on Sunday. “I worked on it. Coming in I didn’t really run an offense like that coming out of college … having to transition into gap scheme and reading holes one at a time, it took a little while to work out. But it pays off once you get to it.”

Kyle’s system borrows heavily from his father’s, and Mike still serves as an informal adviser to the 49ers who watches all the coaches’ meetings on video. More than half of San Francisco’s rushing attempts through Week 15 came on zone plays, according to ESPN. Like all of their other offensive snaps, the 49ers dress up their zones with tons of motion. While the average NFL team motioned a player before the snap on slightly less than half of its plays (47 percent), the 49ers do it 78 percent of the time, according to Pro Football Focus, easily the highest mark in the league. Moving around tight end George Kittle, fullback Kyle Juszczyk, and receiver Deebo Samuel, among others, helps confuse defenders about what is coming and can also clear them out of the way before a play even starts.

The holes don’t last long, but if the running back gets there in time, they can be massive. Here’s the zone play the 49ers used on their final snap of Sunday’s first half, on which Mostert scored his third touchdown. Mostert was hardly touched.

Mostert’s fourth touchdown also came on a zone run, this time to the outside.

He isn’t touched by a Packers defender until he’s already 12 yards downfield. The 49ers want to get Mostert to the sideline on a wide zone, and the defense needs one defender to force Mostert back inside. No one on Green Bay does that. Most of its front seven get caught in the moshpit of linemen at the 20-yard line, and Mostert has a rushing lane so big it’s more of a rushing highway.

The lesson, as always: Nothing good happens in a moshpit.

Here’s another outside zone, but this time a Packers defender forces Mostert back inside. Still, Green Bay’s defense is stretched so thin that Mostert easily cuts up the middle of the field. Once he clears the initial wave of defenders, he can scamper virtually untouched between his own 35- and the opposing 45-yard line.

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Later in the second quarter, Mostert made a similar cut upfield on an outside zone run for another 11-yard gain. Once again, look how big the hole is.

“You don’t see holes that big in this league,” announcer Troy Aikman said after the play. “But it seems like whenever you watch the 49ers you see several of those each and every week.”

During the regular season, San Francisco was tied for second in 20-plus-yard runs (16) and fourth in 40-plus-yard runs (4). In two playoff games, the 49ers already have four 20-plus-yard carries—more than the Dolphins or Jets had all season. Mostert traveled an average of 11.3 miles per hour when he crossed the line of scrimmage this season, the second-fastest mark in the league after Lamar Jackson. Mostert isn’t trying to avoid defenders at the line of scrimmage—he’s trying to get up to full speed because the only thing in front of him is grass. Mostert led all running backs in yards before contact per attempt (3.5); fellow Niners back Matt Breida ranked second (3.3) and Tevin Coleman also cracked the top 10 (2.6). As a team, the 49ers had more rushing yards before contact than the Steelers had rushing yards total.

The Chiefs defense stopped Derrick Henry in last weekend’s AFC championship game, but the 49ers present a different challenge. Henry is big and bruising; the question is whether anyone can tackle him. With Mostert, the question is how far downfield he’ll be when the Chiefs even touch him. More than two decades ago, Terrell Davis was named Super Bowl MVP as the first star of the Shanahan zone-running system. Less than two weeks from now, the next star of that system could follow the same path.