Darnell Dockett Signing Gives 49ers the Ultimate Boom-or-Bust Defense in 2015

Even while the San Francisco 49ers struggled during the 2014 season, their defense was solid. An inconsistent offense ranked 25th in scoring and was held to 10 or fewer points on three occasions, and the D was crushed by injuries and suspensions, yet only four teams allowed fewer points and only three created more turnovers than San Francisco. 

But they're getting healthier now, and they've replaced departed headache defensive end Ray McDonald with three-time Pro Bowler Darnell Dockett, who signed a two-year, $7.5 million contract this week, according to ESPN.com's Josh Weinfuss. 

It's all quite promising as they prepare to regroup under the leadership of new defensive coordinator Eric Mangini. But this continues to look like a defense that could go belly-up just as easily as it could dominate in 2015, with Dockett epitomizing that boom-or-bust nature. 

San Francisco will have the best defense in the league next year, if...

If Dockett can return to his 2013 form

That was the last time we saw Dockett at or near his best. Only seven 3-4 defensive ends had more stops than him that year, according to Pro Football Focus, and he supplemented strong run defense with 4.5 sacks and 13 quarterback hits. The latter number ranked fourth among players at his position. 

Player	Hits
J.J. Watt	36
Calais Campbell	17
Kyle Williams	17
Darnell Dockett	13
Cameron Jordan	13

But then Dockett tore his right ACL just weeks prior to the 2014 season, which isn't as easy to come back from when you're 33 years old. The 11-year veteran never played another game in Arizona and should now only be expected to contribute as part of a rotation in San Francisco. 

That's nothing new for the Niners, who used another stud defensive end, Justin Smith, in a similar fashion in 2014. Smith started all 16 games but played only 67 percent of San Francisco's defensive snaps. Which leads us to another if...

If Justin Smith returns at all

The five-time Pro Bowler had 21 stops, only three missed tackles, five sacks and a pair of forced fumbles as a semi-full-time player in 2014 and is only a year removed from an All-Pro campaign, but Smith will be 36 in September and could be contemplating retirement. 

Player	Age
Charles Woodson	38
Justin Smith	35
Rashean Mathis	34
Calvin Pace	34
Julius Peppers	34

He was slated to meet with head coach Jim Tomsula this week, according to Matt Barrows of The Sacramento Bee, who notes that "there has been cautious optimism he will return for one more season." If that happens and Dockett can stay healthy, it'll make things a lot easier on an inevitable rotation of less proven players inside. 

If they can get healthy at nose tackle

Before Ian Williams went down with a season-ending leg injury in Week 10, he was graded by PFF as the best nose tackle in the NFL. With former top-five pick Glenn Dorsey also missing the season due to a biceps injury, it's amazing the 49ers ranked seventh against the run. 

A rotation featuring Dockett, Smith, Williams, Dorsey, Quinton Dial, Tank Carradine and Tony Jerod-Eddie would be as deep as they come up front. And that's just the defensive line. The linebacking corps could be even stronger. But alas, more ifs...

If NaVorro Bowman and Patrick Willis can bounce back

The superstar inside linebacker duo played in only six of a possible 32 games last season, with Bowman missing the entire year after tearing the ACL and MCL in his left knee in the 2013 NFC Championship Game. One year prior, the 26-year-old was PFF's highest-ranked pass-rusher among qualified inside linebackers. 

Player	Total
Patrick Willis	5
NaVorro Bowman	3
Dwight Freeney	3
Julius Peppers	3
John Abraham	2

Willis missed the final 10 games of the season after undergoing toe surgery. The five-time All-Pro hadn't been performing at an exceptional level, but he's only 30 and should be able to contribute in a big way if he can remain healthy. 

It helps that there'll be less pressure on Bowman and Willis thanks to the emergence of young studs Chris Borland and Aaron Lynch. And another if...

If Chris Borland and Aaron Lynch can avoid sophomore slumps

In last year's draft, 76 players were selected ahead of Borland, and 149 went off the board before San Francisco picked Lynch. But had Borland played a full season, he might have been Defensive Rookie of the Year, and Lynch led all rookie outside linebackers with six sacks and 40 pressures.  

Despite playing less than half of San Francisco's defensive snaps and starting only eight games, Borland was graded by PFF as the best run-stopping inside linebacker in football. He was a tackle machine who deserves more playing time. 

The "problem" is that it'll be very hard for San Francisco to get Bowman, Willis and Borland on the field at the same time, especially if Lynch, veteran Ahmad Brooks and Aldon Smith keep rolling at outside linebacker. 

But considering the injury issues this defense has faced, the more quality players the merrier. Oh, and discipline issues, which leads us to our final if...

If Aldon Smith can get his act together

It's also amazing the Niners were able to fare so well defensively last season considering the distractions coming from dudes like McDonald and Smith, the latter of whom had a ridiculous 33.5 sacks during his first two seasons in the league before dealing with off-field issues in 2013 and 2014. 

Seasons	Games	Sacks	PFF grade
2011/2012	32	33.5	66.4
2013/2014	18	10.5	33.8

Smith was arrested on suspicion of driving under the influence and possession of marijuana in September 2013, spent some time in a rehabilitation facility and was suspended for nine games after being arrested in relation to an incident at the Los Angeles International Airport the following offseason. 

As a result, 2011's seventh overall selection has played only 47 percent of San Francisco's defensive snaps the last two seasons. The emergence of Lynch takes some pressure off him, but if Smith can get back on track as a situational pass-rusher, he could put this D over the top in 2015. 

Deep and complicated

Basically, they're loaded with talented question marks on defense, which is never ideal. But if Tomsula and Mangini can keep everyone focused and the injury gods can treat them well, the 49ers are in position to challenge the Seattle Seahawks for the league's best defense in 2015. The Dockett signing adds a question mark, but also adds potential. 

Brad Gagnon has covered the NFL for Bleacher Report since 2012.