The San Francisco 49ers win a lot of games because of their defense, and their defense is led by some incredible linebackers.
Patrick Willis, NaVorro Bowman, Aldon Smith and Ahmad Brooks helped lead the 49ers to Super Bowl XLVII last season. All four lit up the stat sheet, as Smith and Brooks combined for 26 sacks and Willis and Bowman combined for 268 tackles.
There's no doubt that San Francisco's linebackers have put up eye-popping numbers so far, and there's no doubt that the young group will continue to pile up numerous accolades. But how valuable is the group?
Middle linebackers breakdown
Bowman and Willis make up the league's best duo of middle linebackers, as both rarely miss tackles. Bowman finished tied for second in the NFL in tackles in 2012, and only 11 players posted more total tackles than Willis. Both did a great job stopping the run, and both did a nice job against the pass.
The two combined for 15 passes defensed and three interceptions, and Willis finished second among linebackers with nine passes defensed. Both players excelled in coverage, and both will continue to do so.
And as they do so, they will carry the defense.
How many Pro Bowls will Bowman and Willis make (combined)?
The two have proved their value in San Francisco, and they have received recognition throughout the league. Willis has never missed the Pro Bowl in his six-year career, and Bowman will assuredly pile up more Pro Bowl appearances.
Willis would have started the 2013 Pro Bowl if the 49ers hadn't made the Super Bowl, and Bowman likely would have started if the 49ers didn't make the Super Bowl and if the team ran a 3-4 defense (which allows two middle linebackers to start). If injuries don't slow him down, he'll likely be on the field in the Pro Bowl annually.
Bowman and Willis are extremely physical, and they are tremendous, well-rounded players. However, they aren't the only top-flight linebackers on the team.
Outside linebackers breakdown
Smith failed to register a sack in his last six games, but he still managed to finish the season with 19.5 sacks.
Will Smith continue to pile up sacks without any injuries limiting him?
A torn labrum limited Smith, and it cost the 49ers defense. San Francisco allowed an average of 29.7 points per game (PPG) in its last six games, and Smith didn't post a sack in any of those games. If that continues into 2013, the 49ers won't win much.
San Francisco went 8-1-1 when Smith registered a sack, and it went 6-1 when Brooks registered a sack. Brooks wasn't dominant, but he defensed eight passes in 19 games and picked up 6.5 sacks. He came up clutch in the NFC Championship Game, as he knocked down a Matt Ryan pass on third down with about one minute left.
Smith also made his presence felt in the game, as he came up with a vital fumble recovery. He didn't apply much pressure on Ryan, but with Smith fully healthy, the pass-rushers will be able to apply pressure on the quarterback consistently.
And that will make all the difference.
If Smith, who amassed 5.5 sacks in one game last year, can play like he did before his injury, the defense will be dominant. The secondary suffered last season because it had to cover receivers for a long time, and that led to the defense's poor numbers.
With rookie Corey Lemonier in the mix, the outside linebackers should apply pressure on the quarterback with ease. In fact, do not be surprised if the group tops its 26-sack 2012 season in 2013.
Middle linebackers' value
Willis and Bowman have put up gaudy numbers throughout their careers, but how valuable are they?
Both are dominant all-around linebackers who are almost carbon copies of each other. Willis weighs 240 pounds and has a 4.51 40-yard dash to his credit, while Bowman weighs 242 pounds and has run a 4.59 40-yard dash.
There aren't any linebackers who are more physical and athletic, and there aren't any linebackers who are more valuable. NFL.com's Gregg Rosenthal highlighted the pair's value with clips of two plays from San Francisco's playoff game against the Green Bay Packers.
Bowman showed off his ability to chase down running backs in the first play, and he showed his value in pass coverage in the second play. Bowman didn't let wide receiver Greg Jennings gain separation, and because Bowman took away quarterback Aaron Rodgers' primary option, Willis was able to swoop in and sack Rodgers.
No team has its middle linebackers play more pass coverage, and that's because Willis and Bowman are capable against the pass. While they don't rush a lot, they are also capable pass-rushers.
Willis only registered 1.5 sacks in 2012 (including the playoffs), but he showed the ability to toss aside a blocker (in this case, it was fullback John Kuhn) and get to the quarterback. Bowman can do that as well, even though his sack totals also are not eye-popping.
It's clear that both are dominant, and it's clear that the young players will continue to deliver punishing hits. As long as the duo stays healthy, it will punish opposing offenses.
Former Cincinnati Bengal Dan Skuta was locked up in free agency, and he will provide depth. Skuta registered 57 tackles in 2011 and 2012 (combined), so he can make plays. He's not elite, but he's a serviceable backup.
Are Patrick Willis and NaVorro Bowman invaluable?
However, he will be playing behind two elite players. No two middle linebackers were ranked higher on the NFL Top 100 countdown than Willis and Bowman, who came in 10th and 37th respectively.
San Francisco's 3-4 defense is spearheaded by its extraordinary middle linebackers. Willis and Bowman are both young, but they are clearly able to carry the defense.
And because Willis and Bowman can do so much, they are clearly invaluable to the 49ers.
Outside linebackers' value
Willis and Bowman are the leaders of the 49ers defense, but Brooks and Smith certainly help it function.
Smith was voted seventh by his peers on the countdown, and he came in ahead of all outside linebackers. That includes Von Miller and Clay Matthews, who combined for 35 sacks in 31 games last season.
Defensive lineman Justin Smith is credited for taking up defenders to help Smith get to quarterbacks, but he isn't the only reason. Smith has perfected moves like the swim move, which led to five of his sacks in 2012.
In addition, eight of Aldon's sacks came off of a bull rush (via Pre Snap Reads), which is a credit to the 260-pound linebacker's strength. Smith knows how to use a plethora of moves and execute on plays designed to give him a lane to the quarterback, which is why his sack totals are so high.
Justin has done a great job two-gapping for Aldon, and he has created numerous lanes for Aldon. However, Aldon's recognition and instant reaction is required to complete the sack. Aldon is physically gifted, and he knows what to do on the field as well.
And that combination has led to his jaw-dropping numbers.
Brooks may not be as good, but he's a nice complement to Aldon. Brooks can make plays in pass coverage and chase down quarterbacks, which is all the 49ers need. Brooks brought down Baltimore Ravens quarterback Joe Flacco in Super Bowl XLVII, and he broke up two key passes in the NFC Championship.
Lemonier is also a stellar pass-rusher, and he can chip in with some sacks as well. Lemonier and Aldon have similar builds, but Lemonier, who ran a 4.60 40-yard dash, is faster.
Do the 49ers have one of the best outside linebacker trios in the NFL?
He also registered 27 reps on the 225-pound bench press (at the 2013 NFL combine), which displayed his impressive strength. Lemonier is physically capable of doing a lot in the NFL, as evidenced by his 15 sacks in his last 21 college games.
The 49ers have depth at outside linebacker, and they have talent. Smith is one of the best linebackers in the game, and his value was proved by the 49ers' struggles when he didn't register a sack. Brooks isn't a star, but he's definitely above-average.
San Francisco's outside linebackers are tremendous, and they will continue to prove their value in 2013.
The 49ers are absolutely loaded at linebacker.
Bleacher Report's NFL 1000 ranked Bowman and Willis as the two best middle linebackers in the game, and it ranked Smith second and Brooks seventh among 3-4 outside linebackers. All four players are remarkable players, and all four will continue to terrorize defenses.
No team benefits more from the play of its linebackers. The 49ers have invaluable linebackers, and they will continue to demolish offenses for years to come. As long as everyone stays healthy, the group will lead a devastating defense.
None of the starting linebackers are 30 years old, and none will regress. That will lead to a multitude of dominant campaigns from the middle line of the defense.