Fantasy Football Stat of the Day: Success against stacked boxes

(Leading up to the 2021 NFL season, FTN’s Tyler Loechner will dive into the fantasy football numbers to bring you his Fantasy Stat of the Day, five days a week.)

Monday, we took a look at which RBs had to face the highest number of defenders in the box on their rushing attempts, on average. New England’s Damien Harris topped the list, closely followed by Kareem Hunt.

Today, we’ll take a closer look at our defenders-in-the-box stat to get a better idea of what impact this actually has on rushing performance. We’re taking a look at RB yards-per-carry averages against the number of defenders in the box.

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5-6 defenders in the box is the sweet spot, but 8 is the breaking point

Here are the average yards per carry for running backs based on the number of defenders in the box from the 2020 season:

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Defenders in Box	YPC (for RBs)
1-4	6.60
5	5.58
6	4.84
7	4.39
8	3.86
9	3.63
10+	1.16

And the above data in chart form:

A few thoughts:

There’s a high correlation between defenders in the box and YPC. If you exclude the grouping of 10-plus defenders in the box, this data has a linear R-squared of 0.95, which shows extremely high correlation between the numbers of defenders in the boxing rushing yards per carry. This may seem obvious, but it’s still an extremely high correlation. It means that the number of yards gained on an RB rush attempt can be almost entirely (95%) explained simply by the number of defenders in the box.
5-6 is the magic number. When the defense features only 5-6 players in the box, RBs can crack around 5 YPC or more.
8 is the breaking point. RBs dip below 4 YPC when the defense features at least 8 players in the box.
It’s a self-fulfilling prophecy at the 10-plus mark. RB performance appears to fall off a cliff when 10-plus defenders are in the box, but this is misleading. There are usually only that many defenders in the box in goal-to-go situations, when the RB can only gain a yard or two, three at most, anyway.