This is the first part of a four part article summarizing the relative importance of each phase of the game in winning.
Passing is much more important than running, and offense appears to be more important than defense. Turnovers matter a great deal, interceptions more than fumbles. Penalties matter too, but not like you’d think.
We've been told by NFL analysts for years that defenses win championships and that a solid running game is the key to winning. I'd agree that things appear that way. Teams with lots of passing yards aren't always winners, but teams with lots of running yards almost always are. But, as you're about to find out, appearances can be deceiving.
One way to measure the relative importance of passing vs. running, or offense vs. defense, is to measure their statistical correlations with season wins. For example, the correlation coefficient of a team's total rushing yards correlates with its number of wins in a season is 0.45. A correlation of 1.0 would be perfect correlation, while a correlation of 0.0 would indicate no relationship. So 0.45 implies that total rushing yards is a moderately strong indication of how many games a team would win.
In comparison, total passing yards correlates with wins at 0.31. Compared with total rushing yards, total passing yards is less important in terms of winning games. This is what most fans and analysts notice when watching games or glancing at team stats. But does this mean that passing is less important than running in the NFL?
Before we settle on an answer, we need to consider the number of attempts of runs and passes. In baseball, the statisticians understood this 150 years ago when they created the batting average. If one player has 300 hits and another player has 350 hits, who is the better batter? The answer is we don't know until we divide the number of hits by their at-bats.
RUN AND PASS EFFICIENCY
How often have you heard an NFL commentator say, "When running back X gets at least Y carries, his team wins?" The clear implication is that the team in question should feed a steady diet of carries to the running back, and this will cause his team to win. What if we stated the same observation this way, "When his team is winning, running back X receives at least Y carries?" And by the way, why don't we ever hear, "When QB X passes at least Y times, his team wins?" Here's why:
The negative correlation for pass attempts means that the more often a team passes, the less likely it is to win. The correlation of rush attempts with wins (0.58) is even stronger than that for total rushing yards (0.45). This is a curious result, and it’s where conventional NFL analysis begins to crumble.
When we see two things that appear correlated, it is natural for us to say that one causes the other. The runs come during the game, and the win comes at its conclusion. Therefore most fans and analysts assume the running causes the winning. The problem is, it usually doesn't. It's the winning that causes the running. Teams that are ahead, and likely to win, run the ball to take time off the clock and to minimize the risk of a turnover. Teams that are behind, and likely to lose, abandon the run in favor of the pass. Statistics can measure the correlation, but it can't determine the direction of causation.
The critical question then becomes: how can we truly measure a team's passing and running abilities and their respective contributions to winning? The answer is football's equivalent to the batting average--efficiency stats. If we want to know how good a team is at running, the best way is to know how many yards it tends to gain each time it runs the ball--yards per rush attempt. The table below lists basic passing statistics and their correlation with season wins.
Yards per pass attempt is merely pass yards divided by pass attempts. So we have a relatively weak statistic (0.31) divided by an even weaker one with a negative correlation with winning (-0.17). We would expect to have a fairly meaningless result, but we don't. Passing efficiency turns out to be strongly correlated with winning (0.61). And unless having a lead in a game ‘causes’ a team’s passes to be more successful, we can safely say that passing efficiency leads to winning.
Because sacks are an important factor in the passing game, I include plays that result in sacks as pass attempts for the purpose of calculating efficiency. Likewise, I also subtract sack yards from total passing yards. I call this true pass efficiency and have found it correlates better with both offensive points scored and wins.
Continue reading part 2 of the article.