Why Foster and Buckner are the two core pillars for an improving 49ers defense

Summer optimism reigns supreme in the NFL, and going into the 2018 season it might be difficult to find a team more confident in its chances than the San Francisco 49ers.

Yes, the team that finished a dismal 6-10 in 2017 with the 20th DVOA, according to Football Outsiders, is dreaming of the Lombardi Trophy.

The good feelings in San Francisco center largely around the offensive genius of Kyle Shanahan, Jimmy Garoppolo becoming more comfortable in the 49ers' offense, and Richard Sherman bringing stability to the secondary. Yet, while the rebuild is progressing smoothly, San Francisco still needs to improve in some key areas - particularly the defense.

After finishing 26th in defensive DVOA last season, there's little doubt that 49ers defensive coordinator Robert Saleh’s unit will improve in 2018. Another year in Saleh’s system means, in theory, the players will be more comfortable and able to play faster and more effectively. Furthermore, the addition of Sherman should positively impact the defense in coverage.

If the 49ers' defense does improve significantly in 2018, two players - Reuben Foster and DeForest Buckner - will almost certainly deserve the lion's share of the credit.

Foster, who is suspended for the first two games of the regular season due to some off-field transgressions, is coming off a noteworthy rookie year. He looked sensational when healthy, but battled a myriad of injuries, forcing him to miss more than 50 percent of the 49ers' defensive snaps.

Foster immediately became one of the league's best young linebackers, finishing eighth in the NFL in run stop percentage, according to Pro Football Focus, with 37 stops and 61 tackles.

Foster’s play speed and instincts give him the ability to shut down opposing offenses all over the field. This play is a great example of what makes him such a great linebacker so early in his career:

Foster lines up directly, or “stacked,” behind the nose tackle at the snap, presumably responsible for the backside B-gap. After the snap, he immediately reads the first steps from the offensive line, quarterback, and running back, known as the “triangle read,” and begins to flow play side.

Unfortunately for Foster, his nose tackle does a poor job of slowing the center’s path to the second level. That allows the center to approach Foster unimpeded, which typically sets the stage for a huge cutback lane, and in this case, a big gain for Cowboys running back Ezekiel Elliott.

Not this time.

Foster quickly evades the block and advances into the backfield, tackling Elliott for a loss. The 24-year-old’s ability to put his foot in the ground, redirect his movement, and dip his inside shoulder to avoid the block against the best center in football, Travis Frederick, illustrates unique athletic ability and upper-body control. Even more impressive is Foster’s skill to read the situation and react quickly with the proper movement patterns.

Foster thrives against the run, and he's strong against the pass, too. The second-year linebacker is surprisingly well-rounded for his age, and will only get better if he can stay healthy.

If Foster is the main pillar of the 49ers' defense, Buckner isn’t far behind.

Listed at 6-foot-7 and 300 pounds with 34.75-inch arms, Buckner is an anomaly in the NFL. The Oregon product uses his considerable size and length to batter and bruise opposing interior offensive linemen.

Much like Jacksonville’s Calais Campbell, Buckner’s favorite way to beat blockers is with the swim move, just like he did here:

The swim move is an effective one for taller defensive linemen because it allows them to utilize their height advantage.

However, it also tends to expose the defender's chest. That's why it's critical for the player to have powerful technique, which allows him to clear contact prior to executing the arm-over, just as Buckner does in the above clip with a violent chop move using his right hand.

Buckner has primarily played in odd-man fronts since college, so switching to an even front in 2017 was an adjustment. With that year of experience under his belt, Buckner should be comfortable with the alignment, angles, and technique of the new defense, allowing him to fully unleash his freakish skills and become a force on every down.

With the regular season on the horizon, optimism will soon give way to reality. And if the 49ers do somehow manage to meet their lofty preseason expectations, Buckner and Foster will be two of the main factors.

John Owning is an NFL writer at theScore. He has written for Bleacher Report and Football Insiders. He was also the lead NFL content editor at FanRag Sports. John provides analysis on the Dallas Cowboys for the Dallas Morning News and edits for The Quant Edge. Find him on Twitter @JohnOwning.