It has been said time and again that the 2009 pass rush was terrible so I'll spare you an intro that rehashes those times. Gene Smith and the rest of the Jaguars front office have done everything they can this offseason to improve the pass rush to a point at which it can be effective and, in an ideal situation, elite in the not-so-distant future. What they surprisingly have not chosen to address is another position of concern for the Jaguars, safety.
Reggie Nelson is far from a fan favorite among Jaguar fans. Although statistically and according to ProFootballFocus's safety ratings, Nelson wasn't the worst of the NFL's starting safeties, it was his susceptibility to bonehead plays that has Jags fans calling for his head. It appears, though, that Nelson will have another year in teal with most, if not all, of the same safety group from 2009. The hope for many is that a revamped defensive line that puts pressure on opposing quarterbacks will assist the secondary and allow for improved play. How much of an impact can we expect a revamped defensive line to have?
My first goal in figuring this out was to find out how each team's safeties performed in 2009. To do this I used ProFootballFocus's ratings for each safety on each team. There is some subjectivity to these ratings; however, they do give a good general guideline as to how each player performs. I then used a formula to determine the average play of the safeties from each team, weighted so that players with more snaps count more towards the average. For example, if a starting safety saw 1,000 snaps that finished with a rating of +10.0 and a backup that saw 200 snaps and finished with a rating of -10.0 the average wouldn't be 0. The average would come to +6.67.
With those numbers for each team, I then plotted them on a graph versus the amount of sacks each team had. With that scatter plot I added a trendline to get an idea as to how much better the safety play became as sacks increased. Here is the chart with the Jaguars unfortunately on the far left due to their league low in sacks:
The formula at the top gives the slope of the trendline and provides the key to figuring out how much sacks help on average. For those who haven't taken algebra any time lately and need a refresher, the formula tells us that for every sack a team records, the average level of play of their safeties goes up by 0.269 points on PFF's rating scale.
Verdict: This system is far from perfect. Just look at the Giants way down at the bottom who finished with a grade of -13.3 for their average safety despite finishing with more than double the sacks of the Jaguars. However, on average it does appear that there is a correlation between the performance of safeties and QB pressure so the myth holds true.
Food for thought: If the Jaguars were to improve their pass rush enough to earn the league average in sacks, the formula tells us that the average performance of the safeties would be -1.41, far from satisfactory, but still close to the league average.
Update:
JLydon37's comment got me wondering too so I added a chart that was weighed for pressures instead of sacks. The slope is much less, but that's also because the amount of pressures are a lot more and stretch the x-axis.
A little unrelated, but some of the numbers were really weird when you compare to the team's sacks. The Chiefs rank 31st in sacks at 22, but rank 14th in pressures at 136. The Dolphins tied for 3rd in sacks at 44, but rank 20th in pressures at 126.
