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Statistically Speaking: Cowboys' O-Line Paving The Way For DeMarco Murray?

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Is the O-line making DeMarco Murray look good, or does Murray add something extra to the Cowboys' ground game?

Tom Pennington

By now, DeMarco Murray has become a household name among all NFL fans, and comparisons with former Cowboys greats like Emmitt Smith and Tony Dorsett are being drawn left and right. Similarly, the Cowboys' rejuvenated offensive line has drawn rave reviews (for the most part) about their contribution to the Cowboys' new-found success on the ground.

To see just how much the blocking is contributing to Murray's overall numbers, we turn to our friends from Football Outsiders. FO have developed two specific metrics to evaluate blocking and rushing performance that we'll look at below.

Adjusted Line Yards:

Based on regression analysis, the Adjusted Line Yards (ALY) formula takes all running back carries and assigns responsibility to the offensive line based on the following percentages:

Losses: 120% value
0-4 Yards: 100% value
5-10 Yards: 50% value
11+ Yards: 0% value

These numbers are then adjusted based on down, distance, situation, opponent, and the difference in rushing average between shotgun compared to standard formations. Finally, we normalize the numbers so that the league average for Adjusted Line Yards per carry is the same as the league average for RB yards per carry [which is 4.11 yards after nine weeks in 2014].

ALY penalizes an offensive line when a runner is tackled for a loss by adding 20% on top of the negative yardage (e.g. a run for -5 yards is credited with -6 yards, or 120% of the original value). It also gives progressively less credit for long runs, simply because the contribution of the line, once the runner hits the open field, quickly approaches zero.

Therefore, the first four yards of a run are fully credited, the next six yards (the running back hits the second level between 5 and 10 yards out) are only credited with half the actual yardage and for all yardage beyond the 10 yard line (the running back is now in the open field) the offensive line doesn’t get any credit at all.

Using Adjusted Line Yards, this is how the Cowboys offensive line performed so far this year, and how that compares to previous years:

Year Rank Adj. Line Yards RB Yards NFL Avg
2012 22 3.92 3.78 4.25
2013 4 4.23 4.66 4.10
Wk 10, 2014 2 4.49 5.02 4.11

Yes, you read that correctly, the Cowboys' O-line didn't suddenly emerge as a top five run blocking unit this year. They were also a top five unit last year (as measured by Adjusted Line Yards). Except the Cowboys didn't run the ball much last year.

You find that hard to believe? Think about it this way: DeMarco Murray, who leads the NFL in rushing with 1,133 yards, is averaging 5.0 yards per run. Last year, when the Cowboys finished last in the league in total rushing yards, Murray had an average of 5.2 yards per run. The Cowboys simply didn't run him much, but Murray ran well enough to make the Pro Bowl.

But what's remarkable about the numbers in the table above is that the Cowboys' O-line was ranked 22nd just two years ago, and moving up into the top five is a significant change in performance, a change that coincides with Travis Frederick and Ronald Leary getting starting spots in the Cowboys' offensive line.

At this point, the Cowboys' offensive line is clearing a path for significant chunks of yardage for DeMarco Murray. So the question is, is the O-line making Murray look good, or is Murray good enough on his own, and does he add anything to the run game that the O-line doesn't already do?

The running backs

You cannot evaluate running backs in isolation from their O-line. But while you can't completely separate the effect the two position groups have on each other, you can approximate it by looking at the relationship between Adjusted Line Yards and Running Back Yards, which are the standard NFL yardage numbers we're used to.

Per the table above, the Cowboys’ running backs are gaining 5.02 yards a pop in 2014, the best value in the league ahead of the Saints (4.72), Ravens (4.64), and Steelers (4.61). That's pretty impressive any way you look at it.

If you deduct the Adjusted Line Yards from the Running Back Yards you'll get a good measure of how the running backs performed relative to the line, because by taking away the contribution of the offensive line, be it good or bad, you'll get a measure of how good a running game a team has. The table below does that calculation for the top six teams in 2014.

Running Back Yards minus Adjusted Line Yards, 2014
Rank Team Adj. Line Yds (NFL rank) Running Back Yds (NFL rank) RBY - ALY
1 Philadelphia 3.25 (30th) 4.36 (8th) 1.11
2 Buffalo 3.33 (29th) 4.01 (19th) 0.68
3 Tampa Bay 3.34 (28th) 3.96 (23rd) 0.62
4 Houston 3.89 (19th) 4.48 (5th) 0.59
5 Dallas 4.49 (2nd) 5.02 (1st) 0.53
6 Pittsburgh 4.09 (13th) 4.61 (4th) 0.52

The team that stands outr the most here are the Eagles, who have one of the worst run-blocking O-lines in the league, yet have a running game that gets a lot of yardage despite its O-line. Remember how ALY doesn't include any yardage beyond ten yards? Teams with an overproportional amount of breakaway runs tend not to look quite as good in this metric.

The Cowboys are right up there in a second tier of teams, all of which have (or had) some pretty dynamic runners on their roster this season. You may not see it in their total yardage or their yards per attempt, but runners for the teams on the list above consistently get more yards than their O-line woud warrant.

A lot of the credit for the Cowboys' success on the ground must go to the offensive line and their blocking. But an equal amount of credit must go to DeMarco Murray, whom Football Outsiders rank as the best back in the league in their DVOA rankings.

Taken together, this has resulted in an almost unprecedented level of excitement about the Cowboys' ground game.

In any case, now that you've seen the Adjusted Line Yards, you'll understand why DeMarco Murray felt he had to get his linemen some presents.