San Francisco's Staunch Defense

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

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7 Responses to “San Francisco's Staunch Defense”

  1. Anonymous says:

    How much luck vs skill is involved in opponent's starting field position?

  2. Keith Goldner says:

    I don't think there is a huge element of luck involved. A combination of good defense, limiting turnovers, and special teams performance will be the biggest factors.

  3. Ian Simcox says:

    Down 19-0 30 seconds into the 4th quarter, facing 4th and 2 from their own 26 yard line, St Louis decides to punt. Three plays later, Smith throws a 56 yard touchdown and it's 26-0. Phew, sure glad you didn't go for it before, you'd have looked silly giving up such a short field.

    7 minutes later, down 26-0 and they're going for it on 4th and 12, on a play which calls for Feeley to drop back and trip over his offensive lineman.

    A few minutes later, and they're punting on 4th and 5, when the game is so dead you might as well go for it to see if you can give your guys some good feeling by scoring a TD.

    The Rams are 2-10. I'm sure that's wholly unrelated to this ranndom punt/don't punt pattern.

  4. Dan Whitney says:

    Football Outsiders has a chart that asses starting field position and it has the 49rs with an average offensive position of 32.38 and defensive position of 24.52 (numbers do not include this weeks games.) Both of these are #1 in the league. These numbers aren't adjusted to strength of schedule but it is still impressive that their net field position is more then 2.5 yards greater than any other team.
    I don't know how predictive or replicable this stat is, but it does seem to inform us why they are wining and if you watch their games it does feel like they are in control of the games because of the field position. They also have the fourth longest time of possession at 32:02 per game.
    Side note- Brian I wonder if TOP might be a valuable stat in your model because it looks like most of the good teams are near the top and the numbers look somewhat consistent with last year's numbers.

  5. bigmouth says:

    Alex Smith is not Trent Dilfer. Come on, man, look at the stats. It's just a ridiculous comparison, lol.

  6. James says:

    Isn't a good offense more important than defense for opponent field position? A good offense is more likely to score (and kickoff to ~20), get closer to the end zone when it doesn't score, and "flip field position".

    I don't even know what a defense can do to affect opponent starting field position.

  7. Joel says:


    Defense can cause turnovers, and negative yardage plays.

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