The San Francisco 49ers' ascension from perennial doormat to potential Super Bowl contender under Jim Harbaugh this season has been well chronicled. Popular perception is that the 49ers have achieved their 10-3 record via the 2000 Baltimore Ravens route: stout defense and a strong running game. Although that's certainly true as far as it goes, a little-noticed catalyst of their turnaround has been a major improvement in pass offense. According to Football Outsiders' measure of play-by-play efficiency, DVOA, San Francisco's pass offense is currently ranked 13th after ranking 25th in 2010.
There are plenty of theories about why the pass offense has improved. It could be the 49ers' conversion to a West Coast offense. It could be that Harbaugh and offensive coordinator Greg Roman are better playcallers than their predecessors. It could be that Alex Smith has finally figured out the NFL passing game after six years of seeming bewilderment. Whatever theory you prefer is a matter of taste, but one explanation that we can rule out as an improvement is the pass blocking of San Francisco's offensive line: the unit ranked 30th in adjusted sack rate (ASR) last season, and ranks 29th so far this season.
If you want one statistic to explain the 49ers' wins and losses, it's this hard-to-believe sack breakdown: San Francisco's given up more total sacks in its three losses (20) than it has in its 10 wins (19). Put differently, the offensive line is allowing nearly four times as many sacks when the 49ers lose. This begs the question: "What's at the heart of the problem, and what does it say about the team's title hopes?"
To answer these questions, I took a look at our game charting database, in which we record various pieces of information that aren't present in the NFL's official play-by-play. As we're still in-season, the database isn't complete for all teams, and only goes through Week 12 at the moment. Nevertheless, there's still a large enough sample size of passing plays to draw conclusions about offensive line play. For instance, we have blown blocks, pass pressures and the number of rushers/blockers for an average of 357 passing plays per team.