This past week, I’ve looked at the reasons why I think yards per carry is an overrated and misleading statistic. It’s just as, if not more valuable, to examine how often a running back is successful, and yards per carry tells us nothing about the distribution of a rusher’s performances.

Today, I want to study running back success rate. What do I mean by that? It’s simply the number of successful running plays divided by the total number of running plays; in other words, it’s the rushing analog of completion percentage. How am I calculating this metric?

Let’s start with the denominator: which rushing plays are included? All rushing plays are included but with one exception: I have discarded all runs (a) on 3rd or 4th down, (b) with greater than 5 yards to go, and (c) where the running back failed to get the first down. If a team calls a run play on 3rd-and-6, I am not going to fault the running back. I will simply discard the play. However, if he actually picks up the first down on 3rd-and-15, I will count the play. Only 3% of rushing plays were excluded using this, but it just “feels” like the right thing to do.

Now, the numerator. We evaluate success rate differently by down.

3rd/4th down: If the players gets a first down, it’s a successful run. Otherwise, it is not (and remember, a 3rd-and-6 run has already been discarded from the sample).

2nd down: There are two ways to have a successful run on 2nd down. If the players rushes for at least 6 yards, it’s a successful run. If a team runs on 2nd-and-15, I’m not going to blame the running back for only gaining 6 yards and leaving the team in 3rd-and-long. So as a rule, all 6+ yard runs on 2nd downs are labeled a success. Alternatively, if the player rushes for at least 50% of the yards needed to get the first down, it’s a success. So a 2nd-and-4 run for 2 yards goes down as a success, as does a 5-yard run on 2nd-and-10. If you don’t gain at least half of the necessary yards to get a first down and you gain less than 6 yards, then it’s an unsuccessful run.

1st down: Similarly, there are two ways to have a successful run on 1st down. Once again, I am using the 6-yard rule, meaning a 6-yard run on 1st-and-20 is a successful run. Alternatively, if the player rushes for at least 40% of the yards needed to get the first down, it’s a success. So a 1st-and-10 run needs to gain 4 yards to be successful. On 1st-and-goal from the 5, the running back needs at least 2 yards for it to be a successful run.

With these thresholds in mind, how did running backs fare in 2018? There were 47 running backs who had at least 100 carries last year; on average, they had a successful run 51% of the time. Gus Edwards was the most successful runner by this metric last year, which is consistent with the results we saw in last week’s heat map. The Ravens rookie benefited from playing alongside Lamar Jackson, and was successful on 64% of his carries last year. The full results below:

One thing we can do is measure how success rate compares to yards per carry. That’s what I’ve done in the graph below for these 47 running backs, showing yards per carry on the X-Axis and Success Rate on the Y-Axis. In general, you want to be up and to the right, but there interesting cases are in the upper left (better success rate, worse YPC) and bottom right (lower success rate, better YPC).

You won’t be surprised to learn that Saquon Barkley and Isaiah Crowell were the two running backs whose YPC greatly outpaced their success rate. Barkley ranked 10th in YPC but 41st in success rate; he’s the (5.01, 43%) dot in the bottom right of the graph. Crowell (15th in YPC, 42nd in success rate) is next to him on the graph at (4.79, 42%). Tevin Coleman (4.79, 45%), Nick Chubb (5.21, 49%), and Matt Breida (5.32, 50%) were all players with really high YPC averages but success rates that didn’t quite match.

On the other side of things are four running backs who you probably wouldn’t group together normally: Jamaal Williams, Leonard Fournette, Alvin Kamara, and Mike Davis. All four had much better success rate numbers than YPC numbers, and perhaps for different reasons, too.

Mike Davis, like Edwards, played with a mobile quarterback which probably helped him a bit (and his teammate, Chris Carson, also had strong numbers). He ranked 23rd in YPC but finished 3rd overall in success rate; he’s at the top of the graph at (4.59, 61%). Right next to him there is Alvin Kamara (4.55, 61%), with nearly identical numbers. Kamara is a star player who benefits from playing in a great passing offense, but he oddly produced almost no big runs last year: he ranked 25th in YPC, but 2nd overall in success rate.

Leonard Fournette ranked 45th in YPC, but was 23rd — so, average — in success rate. He’s at (3.30, 51%), edging towards the upper left of the chart. Fournette’s three longest runs of the year went for just 25, 20, and 16 yards. It’s impossible to have any sort of meaningful YPC average with no long runs, but the success rate numbers are a sign that Fournette’s future may still be bright. He was a solid short-yardage runner (8/10 on 3rd/4th-and-3 or less) and had some success on early downs. The big questions with him going forward is can he stay healthy, consistently produce, and produce more big plays.

Finally, we have Green Bay’s Jamaal Williams, who was bad in terms of YPC (36th) but solid (11th) in success rate. He’s the outlier on the upper left part of the graph in between Fournette and Kamara/Davis at (3.83, 56%). His Packers teammate Aaron Jones led the NFL in YPC, but shockingly, the duo had nearly the same success rate! Jones had some long runs — which is of course a plus — but my suspicion is the disparity between the two backs isn’t nearly as large as their YPC averages indicate.

What stands out to you?