Running Back Metrics That Matter - NFL NextGen Stats

It's been a month--a full month!--since the last time we took a look at our beloved running backs. I don't think there is a hotter topic of discussion between pro- and anti-analytics than rushing. The guys fighting for stat-supremacy are all about using the passing game as much as possible while ditching the run; the folks attaining to classic knowledge are all preaching the "establish the run" mantra. Numbers are numbers, and numbers don't lie. You can twist them, but looking at them objectively, numbers say that no matter what, rushing the ball is almost always a worse option than passing it in today's game.

To gain the biggest edge in your fantasy football league, it's necessary to understand how to apply the advanced statistics being used in every sport nowadays. Back in the day, it was all about wins and losses, passing yards, and touchdowns scored. It is not that those stats are worthless, but they don't offer enough to the savvy analysts. While football is yet in its infancy in terms of analytics compared to baseball, the evolution the sport has seen lately in those terms is notable.

Each week, I'll be tackling NFL's Next Gen Stats, bringing you data from the just-completed week's games with notable takeaways you should consider when assessing fantasy players for the upcoming week. In case you're new to the series, or Next Gen Stats altogether, I recommend you read our preseason primer. Now, let's get to the data!

Which Advanced Metrics Matter Most for Fantasy?

Back in mid-September, I took the first look at running backs. I focused mostly on two advanced metrics provided by the NFL: Efficiency (EFF) and Time Behind the Line of Scrimmage (TLOS). Here is a quick refresher.

• Efficiency (EFF) tells us the total number of yards (both vertical and horizontal) the rusher traveled in comparison to the vertical yards he gained. If he gains 10 yards traveling another 10, we know he ran a straight line forward for an Efficiency of 1.0. If he gained 10 yards but traveled 20 total yards, he had a 2.0 Efficiency as 10 of those 20 yards didn't give his offense any real advancement up the field. The lower the number, the more a North/South runner.
• The Time Behind the Line of Scrimmage (TLOS) metric tells us the amount of time a rusher spends before crossing the Line of Scrimmage, no matter if the RB uses that time standing still in the back of a lineman waiting for an opening, or just moving east/west trying to break through some hole.

Those are the two most straightforward metrics that I explored, and probably also those easier to understand when reading tables full of players' stats. We would also come with at least a vague idea in mind that James Conner would be one of the less efficient rushers (he tends to find lateral spaces, out of the box), or that Frank Gore would be one of the most efficient ones (he runs head-down through the offensive line trying to punch his way forward). At the same time, we could expect Le'Veon Bell to have a high TLOS, while the very same Gore wouldn't be wasting much time in the pocket.

All of that is good, and it actually turns to be true when looking at the numbers. But which are the really important advanced metrics to take into account in fantasy football? Which of them correlate more with running back success and fantasy points?

Now that we're through six weeks of play, I'm confident running some simple correlations to see what matters most. Here is a simple chart with the metrics presented in NFL Next Gen Stats web and their relation with the PPR-format points of those running backs included in the data set (min. 30 carries):

As you see, the importance of each metric varies widely. To make things simple, those numbers range from negative-1 to positive-1. Zero means no correlation. A negative value means an inverse relationship (when one metric goes up, the other goes down), and a positive value means a direct relationship (when one metric goes up, the other goes up too).

Instead of giving a quick takeaway of each metric, I'll do it at the same time as I provide you with the leaders and trailers of each category so you can both take the main takeaway from each stat and also see some real-life examples to make sense of it. I'll include the average fantasy points of each player showcased to provide a better fantasy football context for comparison.

"EFF" Translated to Fantasy Football

Leaders and trailers:

Impact on fantasy football points (3%): Efficiency only explains 3% of fantasy points (correlation of 0.03), so it can be straight skipped when assessing players to add/drop/trade/etc. in your leagues. Each rusher has a running style they have developed for years, and it's clear it doesn't have much to do with how many points they produce weekly.

Important takeaways:

• The list above, although small, proves the aforementioned point. It looks like a bunch of random names were pasted in it without much reasoning behind it. Great rushers as Christian McCaffrey or Saquon Barkley are at the top, but so are middling ones like Gus Edwards or Latavius Murray.
• The same happens at the bottom of the leaderboard. Ekeler is an RB2 this season and one of the least efficient rushers. Same with Aaron Jones. On the other hand, Sony Michel or Miles Sanders rank close to them but aren't averaging even half their fantasy points.
• Don't get caught up in EFF. No matter how north/south a rusher is, it doesn't have anything to do with how many points he'll hand you weekly.

"TLOS" Translated to Fantasy Football

Leaders and trailers:

Impact on fantasy football points (34%): I was a little surprised at such a high relation here, but thinking about both TLOS and success, you can make sense of it. The more time a rusher spends behind the LOS, the more patient he is and the best holes he'll find. This can obviously turn into a loss of yardage if the line collapses, but those who wait for the best paths instead of just bull-rushing forward do better in fantasy.

Important takeaways:

• As I said earlier, this list was easy to forecast without knowing anything about the data. Ground and pound players such as Frank Gore and Peyton Barber don't waste time in the backfield. They go straight ahead and try to run defenders over.
• Crossing the LOS quickly doesn't mean a player is bad for not waiting for a better option to open. McCaffrey is the best player in fantasy football and he's just not waiting a lot to produce points on the ground.
• With the exception of Tony Pollard (of those to appear in the list), all other "slow/patient" rushers are virtually averaging 15-plus points per game.
• Among the 46 players in the dataset, there are 14 averaging fewer than 10 points per game. Eight of them rank inside the 12 slowest players.
• I highlighted the main take about TLOS on the impact paragraph, though. Patient rushers get the best results for fantasy owners. If you are debating between adding two players, keep in mind how patient they are or how good their offensive line is. The more time a rusher is given to get the best possible path forward, the better the results.

"8+D%" Translated to Fantasy Football

Leaders and trailers:

Impact on fantasy football points (negative-14% with a grain of salt!): There is a lot of talk around the "stacked box" concept. It is applied when rushers face defensive fronts of eight-plus men. You would think the more defenders in the box, the higher the chances they stop the run. That is not entirely the case and stacked boxes don't affect fantasy football production that much. (Grain of salt: the correlation between 8+D% and PPR drops to just 8% when considering just RBs averaging at least 15 fantasy points)

Important takeaways:

• Stacked box data can be misleading if taken as it comes. Think about it: a lot of rushers face stacked boxes constantly because they mostly run on goal-line situations, thus the packed defense and the lesser production.
• Also, defenses can put more men in front of rushers if they know the runners lack the ability (Jonathan Hilliman), run straight (Frank Gore), or play behind strong offensive lines (San Francisco).
• Teams with bad offensive lines (Arizona, Kansas City, Cincinnati) don't call for great amounts of defenders in the box going against RBs. That is part of the reason why Mixon and the Chiefs' backfield see low 8-D% on average, combined--at least in the case of Kansas City and Arizona--with the fact that some offenses air the ball out many times efficiently also calls for more precaution.
• At the end of the day, I wouldn't pay a lot of attention to stacked boxes when deciding who to play in fantasy football. It looks like an overcomplicating metric that adds noise to the equation instead of making things easier. Take to simpler and more straightforward stats to assess your running backs.

"ATT/YDS" Translated to Fantasy Football

Leaders and trailers:

Impact on fantasy football points (72%): There is nothing you've heard more when navigating through fantasy football websites than this vital point: volume is key. And indeed, it is. The highest of correlations between any NGS metric and fantasy production comes from rushing attempts and rushing yards. Rushing yards are direct contributors to fantasy points (one point per 10 yards, normally), but while attempts don't award actual points, attempts are the stat that explains fantasy points to the higher percentage.

Important takeaways:

• Let me say it again: volume is key. If your running backs are not getting carries, they are basically not getting chances to score fantasy points. Plain and simple. Look for running backs that play in teams that are letting them run with the ball a lot and trusting them often, there is not much more than that to it.
• Just take a quick glance at the table above. Leaders at the top, all green. Trailers at the bottom, all red. Really, don't overthink it: opportunity matters the most.
• As we will see next, there is a much higher relation between attempts and fantasy production than Y/A and fantasy points.

"Yards Per Attempt" Translated to Fantasy Football

Leaders and trailers:

Impact on fantasy football points (11%): When you have to decide who is the best fantasy running back, don't focus on his yards per attempt production without first looking at his volume of attempts. It doesn't matter how high the yardage a player is averaging is if he doesn't get opportunities to run. Always bet on the player seeing more carries than that rushing more yards per carry.

Important takeaways:

• Where is the value of a player than runs for a lot of yards each time he carries the ball if he doesn't carries the ball often? That's the main thing to keep in mind before getting wowed by high Y/A values.
• Always remember: Yards per Attempt alone doesn't mean anything. You need context (rushing attempts) to make them valuable when assessing how good a player is for your fantasy football team.
• Yards per attempt regress to the mean once the volume starts to pile up: Why do you think Duke Johnson and Saquon Barkley have such exaggerated values at this point in the season? Correct, they have rushed the ball only 37 times each.
• Only true studs maintain high Y/A values even on high volume: so far this season, of players with at least 100 rushing attempts, just three players are averaging 5.0 or more yards per attempt and all of them are averaging 18-plus fantasy points per game too.
• Don't put that much weight on high Y/A relating to great players when looking for the next big thing, though. In 2018 there were 71 players with at least 80 carries. Of the 71, only 13 finished with 5.0 Y/A and just five broke the 20-plus fantasy points per game barrier. Lower your threshold a bit, we're entering Week 7 already!

That's it for today. Until we meet again next week, don't get too mad at the bye weeks leaving four teams out of the schedule, try to find the best free agents on your leagues' player pools, field the most productive teams you can and win the weekend with all of your squads!

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