So far in this series on the reliability of Yards After Catch (YAC), I’ve found that it stabilizes in 22 games for TEs and 31 games for WRs. For both positions, that’s slower than it takes for Average Depth of Target (aDOT) to stabilize. In this post, we’ll find out whether or not RB YAC stabilizes faster than for the other two positions; and if so, if that’s also faster than RB aDOT.
As always, below is the standard procedure I use to determine a stat’s stabilization point; this time applied to RB YAC:
- I collected YAC data for all RBs that played at least 8 games for the same team from 2006 to 2016.
- Starting with RBs that played 8+ games for the same team, I randomly selected two sets of 4 games for each RB and calculated their YAC in both sets.
- I calculated the split-half correlation (r) between the two randomly-selected sets of games.
- I performed 25 iterations of Steps 2 and 3 so that r converged.
- I repeated Steps 2-4 in 8-game intervals, from 16+ games all the way to 72+ games.
- For each “games played” interval, I calculated
- I calculated a weighted average of the results from Step 6.3
Results and Discussion
Below is the stability table for RB YAC:
|Games||n||r||R2 = 0.50||Avg YAC||Obs 9.00 YAC|
As the “Wtd Average” row shows, RB YAC takes 47 games to stabilize, which translates to 80 receptions, 101 targets, and 613 routes run. Here’s how that compares to the RB receiving stats I’ve analyzed previously:
- Yards per Target (YPT) = ∞ games, ∞ targets, ∞ routes
- Touchdowns per Route Run (TDPRR) = 81 games, 175 targets, 1,063 routes
- Yards per Route Run (YPRR) = 24 games, 52 targets, 308 routes
- Average Depth of Target (aDOT, aka air yards) = 14 games, 29 targets, 177 routes
- Receptions per Route Run (RPRR) = 13 games, 28 targets, 169 routes
- Targets per Route Run (TPRR) = 12 games, 26 targets, 161 routes
So the good news is that YAC isn’t the least reliable RB receiving stat. The bad news is that it’s third-worst, as well as the fact that two other yardage-related stats (i.e., YPRR and aDOT) stabilize in half as many games or fewer.
But let’s step back for a moment and put the various YAC stabilization points (i.e., games, receptions, targets, and routes) into proper perspective. Because statistics suggests that offensive football is a top-down game, with player performance relying heavily on schemes and play calls devised and implemented higher up the food chain, my reliability analyses look at player-team tenures (e.g., stats from Matt Forte’s tenure with the Bears are analyzed separately from stats from his tenure with the Jets). My data contains 935 such RB tenures, but only 128 — or 13.6 percent — of them involve at least 47 games, 80 receptions, 101 targets, or 613 routes run.4
What’s more, if we look only at active tenures heading into 2017, then only 18 RBs have amassed at least 47 games, 80 receptions, 101 targets, or 613 routes run with their current team. In alphabetical order, they are Le’Veon Bell, Giovani Bernard, Isaiah Crowell, Andre Ellington, Devonta Freeman, Jeremy Hill, Mark Ingram, Duke Johnson, Doug Martin, LeSean McCoy, Jerick McKinnon, Bilal Powell, Theo Riddick, Darren Sproles, Jonathan Stewart, Chris Thompson, James White, and T.J. Yeldon.
And just to be crystal clear as to why the above is important, remember that what I’ve just detailed are the base rate and current count of RB tenures for which Actual YAC represents at least 50% skill. In other words, for about 86 percent of all RB tenures and for all but 18 current RB tenures, the YAC we’ve observed to date is at least 50% luck — and a vast majority of the time a far higher percentage than that.
Speaking of which, after converting Actual YAC into True YAC for 2016, below are the standings for all RBs that played at least 25 percent of snaps per Pro Football Focus:
|Player||Tm||G||Rec||Actual YAC||Rk||True YAC||Rk|
|Jonathan C. Stewart||CAR||13||8||9||17||7.9||28|
|David A. Johnson||ARZ||16||80||8||32||7.9||30|
In contrast to what we saw with True WR YAC vis-a-vis True WR aDOT, the top of the True RB YAC standings doesn’t exhibit a clear distinction between YAC-specializing, short-zone route runners and other types of receiving backs. That’s, of course, because all RBs are predominately YAC-specializing, short-zone route runners. This lack of distinction — coupled with RB aDOT being far more reliable — means you should primarily rely on aDOT when trying to predict a RB’s receiving future.
Nevertheless, for the sake of completeness, I’ll do the same thing I did for WRs, identifying players that meet the following criteria heading into 2017:
- Top-36 True aDOT in 2016
- Top-36 True YAC in 2016
- On the same team as 2016
- Top-3 on the current depth chart for 2017
The initial list contains 11 RBs, but 4 of them experienced a change at head coach and/or offensive coordinator (Tevin Coleman, Devonta Freeman, Devontae Booker, and Todd Gurley), and 2 of them saw competition brought into the fold (Spencer Ware and Jamize Olawale). That leaves five RBs who truly — pun intended — fit the bill (in True YAC order): Jordan Howard, James White, Damien Williams, Duke Johnson, and David Johnson.
DT : IR :: TL : DR
The present reliability analysis tells us that a RB must log 47 games (or 80 receptions or 101 targets or 613 routes run) before his Actual Yards After Catch (YAC) reflects less than 50% luck. In terms of yardage stats for the position, while this is faster than (the awful) Yards per Target (YPT), it’s slower than Yards per Route Run (YPRR) and Average Depth of Target (aDOT). To put this in perspective, and based on my dataset, the probability that a given RB will log enough games (or receptions or targets or routes) with a given team to overcome YAC being mostly luck is a mere 13.6%.
The formula is (Games/2)*[(1-r)/r]. ↩
The formula is [(Observed Performance * Games) + (League-Average Performance * Stabilization Point)] / (Observations + Stabilization Point) ↩
Weighted by group size. ↩
I’m fully aware that the “true” percentage is almost certainly higher because some inactive RBs would have reached one of the thresholds if I had data from prior to 2006 and some active RBs will reach one of the thresholds in the coming years. ↩