San Francisco fans are now questioning Jim Harbaugh's decision to defer enforcement of a penalty on a successful field goal that would have given his offense a first down deep in Dallas territory. Taking points off the board is often the smart play, so did Harbaugh make a good call?
On 4th and 1 with 11:16 in the 4th qtr, 49ers kicker David Akers booted a 55-yard FG to put his team up by 10. Cowboys linebacker Keith Brooking was flagged for a 'leverage' penalty, meaning he used teammates to help elevate himself attempting to block the kick.
As I understand the rule, Harbaugh had the option of accepting the penalty for a 1st down at the Dallas 22 or deferring enforcement to the ensuing kickoff. He chose to forgo the 1st down, take the 3 points, and take the 15 yards on the kickoff.
The 15-yard enforcement on the kickoff ensures a touchback. By taking the 3 points, the 49ers have a 10-point lead with the Cowboys having a 1st down at their own 20. This gave the 49ers a win probability (WP) of 0.90.
Accepting the penalty for a 1st down gives the 49ers the ball at the Dallas 22, up by 7. This is worth a WP of 0.91.
The percentage play would have been to take the points off the board and accept the 1st down, but just barely. In the grand scheme, this is a very small error. The common punt or FG attempt on 4th and short in most game situations is usually more costly, and most fans and analysts hardly take note of them.
To put the 0.01 WP error in context, on SF's following possession that resulted in a 3-and-out, EB Frank Gore gained 2 yards on 1st and 10, costing 0.01 WPA. Had he gained 4 or 5 yds, he would have broken even in terms of WP. So the error is no worse than the difference of a couple yards on first down.
I can see why Harbaugh felt comfortable with a 10-point lead. It meant the Cowboys would need a TD drive, a stop, and another scoring drive. A TD and then a last minute FG only gets Dallas a 50/50 shot in OT. Unfortunately for the 49ers, that's exactly what happened, and OT went the Cowboys' way.
Edit: I should have pointed out that the real mistake was not going for it on 4th and 1 from the 37. It's a no-brainer. Going for it gives the 49ers a 0.87 WP, and attempting the FG gives them a 0.84 WP, for an error of 0.04 WP. See below for the calculation.