Uncertainty defines 49ers defense entering 2015

Fooch's Note: The 2015 49ers Almanac is now available for purchase. It features 14 articles covering Colin Kaepernick, Torrey Smith, the defense, the rookies and so much more. This article is a sampling of what you'll find in the Almanac. It is not the full article, but rather  Head HERE to purchase it.

Change is an unstoppable force in today's NFL. Every season, win-loss records rise and fall, sometimes dramatically. Bottom dwellers ascend to playoff berths and preseason contenders tumble down the standings. That change is fueled by, among other things, the hundreds of players and coaches who are redistributed among the league's 32 franchises each offseason. And yet, for several seasons, change largely left the San Francisco 49ers' defense alone.

Under defensive coordinator Vic Fangio, a suffocating 49ers defense was one of the few things you could reasonably expect to remain constant from one season to the next. From 2011-14, only the division rival Seattle Seahawks surrendered fewer points than the 17.4 per game allowed by Fangio's unit. More advanced measures of performance, such as Football Outsiders' DVOA, shared a similar sentiment; the 49ers posted a top five defensive DVOA in three of the past four seasons.

The consistent success enjoyed by Fangio's defense was due in no small part to the continuity of its personnel, the core of which formed one of the most dominant front sevens in football. Everything revolved around the versatility provided by Patrick Willis and NaVorro Bowman in the center of the defense, who teamed up to give San Francisco the league's best inside linebacker duo. Aldon Smith, when not sidelined by off-the-field issues, terrorized quarterbacks off the edge and led the best 49ers' pass rush since the late 1990s. And bringing everything together was Justin Smith, who anchored a stout defensive line that occupied blockers and allowed the 49ers' supremely talented linebackers to fly around and make plays. Together, those four players experienced unprecedented levels of success; the 49ers became the first team in NFL history to have three first-team All-Pros in their front seven in back-to-back seasons (2011-2012), with the quartet combining for a total of seven All-Pro selections over the past four seasons.

But now all of that feels like a distant memory; the 49ers defense as we've known it is gone. Change finally caught up with them.

Justin Smith retired. Shockingly, so did Willis. Losing the two most important members of the defense was bad enough, but a number of meaningful role players won't be back in 2015, either. Smith's bookend on the defensive line, Ray McDonald, was cut near the end of the regular season after a pair of domestic violence-related arrests. Last year's starting cornerbacks, Chris Culliver and Perrish Cox, both tested the open market this offseason and found employment elsewhere. And perhaps the 49ers' most promising young defender, linebacker Chris Borland, decided an NFL career wasn't worth the potential risk to his long-term health and called it quits after just one season.

To the credit of general manager Trent Baalke, the 49ers aren't entirely ill prepared to deal with the losses suffered this offseason. Baalke has used recent drafts to stockpile talented young defenders on the bench — entering training camp there are 14 defensive players on San Francisco's 90-man roster who have been drafted since 2013, and eight of them were chosen in the first four rounds. However, for a variety of reasons, very few of them have received a meaningful number of snaps to this point. Eric Reid became a day-one starter at safety. Injuries and poor performance from players ahead of them on the depth chart gave Aaron Lynch and Dontae Johnson an opportunity for extended playing time last year, and each approached 50 percent of the team's defensive snaps. Beyond those three, we've seen very little of San Francisco's recently drafted defenders. That will change in 2015. As many as a dozen of the 49ers' recent draftees could realistically claim a meaningful role between now and the start of the regular season. But for now, the dearth of playing time clouds our ability to project what those players will do as they move up the depth chart.

Even setting aside the unknowns involved when dealing with younger players, a number of complicating factors figure to make integrating them into the defense more difficult than in years past. For starters, the sheer volume of turnover on San Francisco's defense over the past seven months is staggering. The number of defensive snaps lost this offseason (4,469) was more than any other defense in football, and nearly matched the total from the previous three offseasons combined (5,023). And it's not like those snaps came from players wasting space on the field — departed defenders accounted for over 40 percent of the team's defensive production in 2014.

When the 49ers did see turnover in previous seasons, it was concentrated almost exclusively in the secondary. Dashon Goldson parlayed his All-Pro bid into a massive payday in Tampa Bay in 2013. Donte Whitner, Carlos Rogers, and Tarell Brown all left the following offseason. Even though each of those players made quality contributions for the 49ers — all but Brown made at least one Pro Bowl — the structure in place on defense made overcoming those departures relatively painless. Fangio had constructed his scheme around San Francisco's star-studded front seven, and that pairing of scheme and talent provided myriad advantages for the secondary.

Fangio could count on the Smiths and the rest of the front four to generate pressure on the quarterback, therefore he rarely blitzed. That allowed seven defenders to drop into coverage on most downs, rarely leaving defensive backs on an island. Willis and Bowman were skilled and athletic enough to blanket opposing running backs and tight ends in coverage, while ensuring the run defense didn't suffer in sub-packages. That freed up the safeties to help on the outside or jump crossing routes over the middle. And on the practice field, one of the league's best secondary coaches, Ed Donatell, was around to develop the skills of new defensive backs entering the lineup. Those advantages allowed the 49ers to plugin new defensive backs into the system without seeing the overall effectiveness of the defense deteriorate.

That structure has almost completely dissipated since the end of the 2014 regular season. Fangio and Donatell will both be coaching in Chicago this year. And as we've already covered, many of the core pieces who made the front seven go are no longer around. Considering the young talent expected to fill the voids, it would be easy to marginalize the impact of each individual loss. But you can't consider each loss in a vacuum, and the cumulative ramifications of having to replace that many key players all at once leaves the 49ers with serious question marks at every level of defense for the first time in years.

To read the rest of this article, order your copy of 49ers Almanac 2015 today. In this chapter of the Almanac, I looked at three questions:

1. Will Tank Carradine finally deliver?
2. Will NaVorro Bowman be the same player post-injury?
3. Can Jimmie Ward become the hybrid defensive back the 49ers need him to be?