Adjusted Line Yards -- the defense
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Last week, we looked at Adjusted Line Yards, Football Outsiders' proprietary statistic, for different NFL offenses. ALY assigns responsibility and value to offensive lines based on the length of a run, the situation, and the opponent. We then drilled down with situational stats that reveal each team's ability to break long plays, extend drives, and avoid negative plays. When you put all those stats together, you get a more complete picture of a line's value to a team.
In that same spirit, we have ALY and other numbers for defensive lines, and the principle is the same. The first step is to separate actual yard per carry from line yards by factoring in play value by situation. Then, we add the percentage of yards on running plays that are 10 yards or more past the line of scrimmage. Power and Stuffed stats illustrate how well defensive lines prevent opposing offenses from creating first downs and touchdowns in short-yardage situations (Power) and put offenses in the hole with negative plays (Stuffed).
The Arizona Cardinals have held the top spot in ALY for most of the season, but after giving up an average of 149 rushing yards in their last three games, they've given way to the Pittsburgh Steelers, and their ALY of 3.19 yards per carry. Pittsburgh also leads the league in yards per carry allowed (3.29). The Cardinals still cause the most negative plays in the game - 31 percent of runs against them are stuffed at or behind the line. No team has allowed fewer conversions or scoring plays on third- or fourth-and-short than the New England Patriots - they stop those plays 43 percent of the time. And if you're looking to bust a big running play, avoid the Miami Dolphins, who have allowed running plays of 10 or more yards only six percent of the time.
Certain teams are just better at bottling up run plays at the line. In addition to the Steelers up top, there's also the Cardinals (3.19 ALY), the Ravens (3.32), Eagles (3.36), and Giants (3.34). As with Offensive ALY, the difference between Adjusted and standard yards can reveal some interesting things.
Teams with similar ALY and YPC are generally good from the line of scrimmage out -- the Chargers, Dolphins, Bengals, Falcons, and Panthers are all in the top ten rank when it comes to fewest percentage of yards allowed beyond the 10-yard mark. These are the teams that don't allow big plays. Correspondingly, teams like the Giants and Texans, who allow almost a yard per carry more in standard yardage, are prone to giving up highlight-reel stuff. The Giants have the NFL's worst 10+ ranking, with a full 33 percent of their rushing yards allowed outside that mark. When you factor in their pass defense, it's reasonable to say that New York's secondary is the thing that could keep them out of the playoffs.
On the other hand, the Giants have an interesting defensive disconnect -- only the Cards have created more negative plays. One in four running plays against the Giants go absolutely nowhere, and it's the same with the Packers, Eagles, and Steelers.
Power success might be the most important stat on paper -- it's based on the percentage allowed of runs on third or fourth down, two yards or less to go, that achieved a first down or touchdown. Any "and goal" situation is also included -- if you stop first-and-goal or second-and-goal, that counts just the same. If you can prevent plays that extend drives and increase scoring chances, odds are you're ahead of the pack. At least, that's what you'd assume -- in addition to the Patriots and Vikings, the Redskins, Lions, and Jaguars are in the top five of fewest Power plays allowed.
The other side of Power is how many big plays of any kind your defense allows -- sometimes, your defense's ability to stand in fewer of those situations simply means that opposing offenses can light you up like a Christmas tree. The Denver Broncos have one of the stingiest defenses in the league, but teams have a 76 percent Power success rate against them. That's why you have to look at the whole picture and how different line stats tell us different things.
By
Doug Farrar
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November 11, 2009; 8:16 AM ET
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