49ers Defense (05/18/15)

By John Ewing Director of Research and Analytics @johnewing
How do the retirements of Justin Smith, Patrick Willis and Chris Borland impact the 49ers' defense?

On Monday the San Francisco 49ers announced the retirement of defensive linemen Justin Smith. The five-time Pro Bowler joins inside linebackers Patrick Willis and Chris Borland as the third member of the 49ers' defense to retire this offseason.

Wear and tear from a 14-year career made the veteran defensive lineman's retirement probable but Smith stepping away from the game, coupled with the losses of Willis and Borland, is a major blow to the 49ers' defense.

How does the retirement of three starters impact San Francisco's defense?

If all three players decided to suit up for the 2015 season we would expect the 49ers defensive unit to allow 21.7 point per game. With Smith, Willis and Borland, San Francisco would allow 4.0 yards per carry and 6.8 yards per pass. The defense would sack opposing quarterbacks on 6.3% of drop backs and have an interception rate of 3.1%. The 49ers average record would be 8.3 wins and 7.7 losses.

Without the three defensive players, the unit is less effective. Point per game allowed (23.9), yards-per-carry (4.5) and yards-per-pass (7.0) increase while sack rate (6.1%) and interception rate (2.9%) decrease. The net result is an additional loss of 1.4 games. San Francisco's projected record after the retirements is 6.9 wins and 9.1 losses.

The 49ers are projected to have their first losing season since 2010.

There are just three defensive starters remaining from the 49ers' 2012 Super Bowl team. When Smith, Willis and Borland retired it not only ended their careers but perhaps signaled the end of an era in San Francisco.

49ers Defense – With and Without Smith, Willis and Borland

Stats With Smith, Willis, Borland Without Smith, Willis, Borland
Points-Per-Game Allowed 21.7 23.9
Yards-Per-Carry 4.0 4.5
Yards-Per-Pass 6.8 7.0
Sack Rate 6.3% 6.1%
INT Rate 3.1% 2.9%
Record 8.3-7.7 6.9-9.1