Why NFC West linebackers did not register

Aaron Schatz's piece on defensive stop rates caught my attention for what it did not include, namely any mention of NFC West players among the highest- or lowest-ranked linebackers.

The San Francisco 49ers' Patrick Willis sets the standard at the position. The St. Louis Rams' James Laurinaitis has emerged as one of the better 4-3 middle linebackers. The Seattle Seahawks' Lofa Tatupu, slowed by injuries recently, also escaped mention.

Taking a closer look at the criteria allowed for a fuller understanding of the statistic. Stop rates reflect what percentage of a player's statistics produce successful outcomes against running plays. The stat defines successful outcomes as those when the opposing runner fails to gain certain percentages of the yards required for first downs. The percentage is 45 on first-down runs, 60 on second-down runs and 100 on third- or fourth-down runs.

So, if Willis tackled the opposing runner after a 4-yard gain on first-and-10, the tackle would qualify as a successful stop because the runner gained only 40 percent of the yards needed for a new set of downs. But if Willis tackled the opposing runner following a 4-yard gain on the ensuing second-and-5 play, his effort would count as a failure because the runner would have gained 80 percent of the yards needed for a first down.

The stat does not necessarily measure how well a specific defender plays the run, but it does paint a clearer picture of where defenders make their tackles in relation to the first-down marker. A player talented enough to make plays all over the field could have a lower stop rate than a player with less range. This likely explains Willis' relatively low stop rate (57 percent).

Schatz provided NFC West-specific information for the charts below. Each player had at least 25 tackles on running plays.

2010 NFC West Stop Rates: Defensive linemen

The stats for linebackers seem to penalize Willis in particular for his ability to make clean-up tackles anywhere.

The 49ers allowed 3.46 yards per rushing attempt, second only to the Pittsburgh Steelers (3.02) among NFL teams.

2010 NFC West Stop Rates: Linebackers

For defensive backs, note that strong safeties ranked higher than free safeties because they generally focus more on run support. Free safeties would be more apt to make tackles well downfield, whether or not they were primarily responsible for allowing the gains.

2010 NFC West Stop Rates: Defensive backs