NFL Analysis: A Closer Look at the San Francisco 49ers Defense

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Three of the members of the Trent Dilfer Club won again this week including Alex Smith, the best parallel to 2000 Trent Dilfer.  The 49ers trounced the Rams 26-0, clinching their first NFC West title since 2002.  San Francisco won the way they have been winning all year: Defense.  The 49ers amassed a -0.37 defensive WPA (negative is good) and did not allow the Rams to pass the SF 38 yardline.  In fact, when the Rams finally got to the 38, A.J. Feeley threw up a pick to Dashon Goldson.  Here's a look at the drive summaries for the Rams:


San Francisco continuously forced St. Louis to start deep in their own territory.  Their best starting field position was at the 23.  According to our Markov model, that would still result in a punt 47.9% of the time.  Check out the starting probabilities for each of the St. Louis drives (you'll notice somewhat of a pattern):

Coming into this week, San Francisco ranked 2nd in the league in average opponent starting field position (between the 25 and 26 yardline).  Further, opponents of the Niners are fairly consistent in their starting field position; San Francisco's opponents rank 5th in the league based on the standard deviation of starting field positions.
Alex Smith once again helped his defense by taking care of the football. He has just 5 interceptions on the year, tied with Aaron Rodgers for the fewest in the league.  Smith posted a +0.09 WPA, most of which (+0.06) came on a 52-yard passing touchdown to Michael Crabtree.
That's what happens when you have a matchup between the league's worst offense and the second best defense.
Keith Goldner is the creator of Drive-By Football, and Chief Analyst at - The leading fantasy sports analytics platform.  Follow him on twitter @drivebyfootball or check out numberFire on Facebook.