has been added.
On all the individual defender stat pages here, I had included SR simply because I already had it coded for teams and offensive players. I thought it might be interesting and possibly reveal something, but no insight materialized. SR for defenders doesn't make sense for the same reason that total WPA or EPA, as derived from play-by-play descriptions, doesn't make sense.
For example, consider two plays involving a free safety. In one play, the safety blitzes, strip-sacks the QB, and returns the fumble for a touchdown. That would be a success under any definition. In the other play, a running back slices through a wide hole on the strong side of the formation, breaks three tackles, and streaks down the sideline until the safety saves the day with a shoestring tackle. Our hero safety would have a SR of 50%, which tells us very little about what really happened.
Instead, let's just add up all the sacks, interceptions, passes defended, QB hits, forced fumbles, fumble recoveries, tackles, and assists that result in team-level successes. Success Count is that simple. The regular season leaders for linebackers in 2010 are Lawrence Timmons, Ray Lewis, London Fletcher, LaMarr Woodley, James Harrison, Cameron Wake, and James Laurinaitis. Not a bad group. SC can tell us a lot more about quality performance without penalizing a player for making plays in some situations.
Put simply, SC is the same concept as SR, but it's a simple counting stat rather than a rate stat. Another way to think of it is "positive plays made."
We could do some other clever stuff with SC. For example, we could calculate 'Success Factor'--something analogous to Tackle Factor (TF). TF measures the proportion of a team's tackles a player makes, which accounts for the fact that worse defenses allow longer drives and make more tackles. TF also compares each player's proportion of team tackles to how many tackles his position should typically expect, which accounts for the fact that some positions will naturally make more tackles than others. Success Factor would account for the same considerations.