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How the 49ers Built Their Defensive Line—and How It Could Wreck the Chiefs

It goes deeper than adding Nick Bosa and Dee Ford in the offseason

Getty Images/Ringer illustration

If football is about winning the turnover battle, then the 2018 San Francisco 49ers lost the turnover war. San Francisco’s 4-12 squad captured just seven turnovers in 2018, the fewest on record for any team in NFL history. It was the worst season in that category by far. At San Francisco’s 2018 pace, the team would have needed nine more games to get to 11 takeaways, the next-lowest mark. In the 80 years of pro football history with reliable data, only 31 teams averaged less than one turnover forced per game. The 49ers became the first team to average less than one turnover every two games.

“That wasn’t fun to watch,” 49ers general manager John Lynch said at a press conference in March. “But it is something we have to live with. It’s a reality, and we needed to change that.”

The 49ers took steps to change that reality in mid-March. Lynch traded San Francisco’s 2020 second-round pick to the Kansas City Chiefs for pass rusher Dee Ford, who led the league in 2018 with seven forced fumbles, and then signed him to a deal paying $85.5 million over five years. Earlier that same week, Lynch had made another big move in signing former Buccaneers linebacker Kwon Alexander to a four-year, $54 million deal. And he wasn’t done. Six weeks later, the 49ers used the no. 2 pick in the draft on Ohio State defensive end Nick Bosa, easily the top pass-rushing prospect of the year.

Bosa and Ford (the no. 23 pick in 2014) joined a defensive line that already had three first-round picks, including the no. 17 pick in 2015 (Arik Armstead), the no. 7 pick in 2016 (DeForest Buckner), and the no. 3 pick in 2017 (Solomon Thomas). That gave the 49ers five first-round picks on their defensive line. Meanwhile, the team did not bring in a defensive back of consequence during the draft or in free agency despite having just two interceptions in 2018, the lowest total since World War II. Lynch, an All-Pro safety in the 1990s and early 2000s, decided the defense would be fine if he quadrupled and then quintupled down on the front six.

“These are the type of players that we believe can reverse that [takeaway] trend,” Lynch said about Ford and Alexander at the March press conference.

Consider the trend reversed. The 49ers finished 13-3 this season, captured the no. 1 seed in the NFC, and are in the Super Bowl in large part because of their defensive line. They’ve gone from worst to first or almost first in a number of categories. In 2018, the 49ers intercepted just two passes. This season, the 49ers intercepted three passes in Week 1. Those picks came from Buccaneers turnover machine Jameis Winston, but the 49ers took the ball away from everyone, not just Winston. The 49ers tied their 2018 takeaway total (seven) in three games. After four games, they were at 11 takeaways, the same number the 2018 squad would have needed 25 games to reach. San Francisco finished with 27 takeaways, sixth most in the league and 20 more than 2018. The difference was that these 49ers created more takeaway opportunities, and that starts with getting to the quarterback.

“Speed and violence affect the quarterback and make people do stupid things before they want to,” Kyle Shanahan said at the same press conference. “Both of these guys [Ford and Alexander] have a lot of speed and they both play very violent.”

San Francisco got into the backfield often. The 49ers pressured the quarterback at a higher rate than every team except the Steelers, according to Pro-Football-Reference. San Francisco had the second-highest quarterback pressure rate despite defensive coordinator Robert Saleh sending the fourth-fewest blitzes (plays of five or more pass rushers) in the league. The 49ers were comfortable with their four pass rushers against five offensive linemen, giving San Francisco’s defense a mathematical advantage in pass coverage.

Disrupting the quarterback paid off. The 49ers were the second-most-efficient defense and pass defense in the NFL this year, according to Football Outsiders. They sacked quarterbacks at the third-highest rate (roughly once every 12 dropbacks), were tied for the second-best defense on third down (33.3 percent conversion), and allowed the lowest passing yards per attempt (5.9) in the league. That also helps the offense. In 2018, the 49ers offense had the worst average starting field position, according to Football Outsiders. This season, it had the second best. Relatedly, they went from no. 25 in touchdowns per drive in 2018 to no. 4 this year.

The Super Bowl features one of the league’s best offenses versus one of the league’s best defenses, and the game may tilt based on how the Chiefs manage to block the 49ers defensive line. Ford has been limited to just two starts this season due to a hamstring injury, but he’s still been effective as a situational pass rusher. (Ford has actually forced fumbles at a higher rate per snap than he did in 2018, according to PFF.) Bosa pressured the quarterback 80 times this season, the most for a rookie edge defender since Pro Football Focus began charting games in 2006. He has shown technique beyond his years while outperforming some of the best tackles in the NFL. One of the handful of defenders who may have outperformed Bosa this year is Armstead, who had 10 sacks while also being one of the better edge run defenders in football. Defensive tackle Buckner is one of the better linemen in the league but the fourth best on his own team. The fifth first-round pick of the bunch, Solomon Thomas, was the surest prospect other than Bosa in the group, but has just six sacks in three years and has made the least impact as a pro. In the NFC championship game, all five of those first-round picks registered a sack, the first time that has happened in a playoff game in pro football history.

The five first-rounders aren’t the only reason the 49ers are talented. They get serious contributions from defensive linemen Ronald Blair, D.J. Jones, and Damontre Moore, but all three are on injured reserve and will miss the Super Bowl. The 49ers pass rush was stronger when they had a pass-rushing rotation that was seven players deep, but the current unit is still elite.

Behind them is a fast linebacker group. Alexander returned in the NFC divisional round from a pectoral injury that had cost him all of November and December. In addition to Alexander, 49ers linebacker Fred Warner is one of the more promising young linebackers in the league. Rookie fifth-rounder Dre Greenlaw has been an excellent contributor, and registered the tackle that changed San Francisco’s season by keeping the Seahawks out of the end zone on Seattle’s final play of the regular season. The 49ers defense is greater than the sum of its parts—and those parts were expensive.

The 49ers are not the first team to add a few pieces to their pass rush and produce a Super Bowl contender. In 2013, the Seahawks signed pass rushers Michael Bennett and Cliff Avril, making the Legion of Boom secondary even better and leading to a blowout of the Denver Broncos, 43-8, in the Super Bowl that season. Denver responded to that game by signing pass rusher DeMarcus Ware to pair with Von Miller, and the Broncos won the Super Bowl two seasons later. Unlike those teams, the 49ers were not a contender when they made these moves in March. San Francisco is just the third team to make the Super Bowl after winning four or fewer games the previous year. Making that turnaround more impressive is how few personnel changes the team needed to increase its takeaways.

To win the Super Bowl, the 49ers may need a few more big plays out of this defense. Chiefs quarterback Patrick Mahomes doesn’t turn the ball over much. He threw an interception on 1 percent of his pass attempts, the second-lowest rate in the league, but the only player who had a lower interception percentage this year was Green Bay’s Aaron Rodgers, who had his first multi-interception game of the season against the 49ers in the NFC championship game.

If anyone can force Mahomes to make some mistakes and do stupid things, it’s this 49ers front. If they can, John Lynch might have fun watching the game.