Kareem Hunt has been bottled up in recent weeks. (Tim Heitman/USA Today)

The NFL season opener in Foxborough was billed as a Patriots celebration. Here was a team fresh off the greatest Super Bowl come back of all time, 10 years removed from their undefeated 2007 season, with prognosticators predicting another such season on the horizon.

Instead, the world was treated to a Kareem Hunt coming-out party. When all was said and done, the rookie had amassed 246 total yards, three touchdowns and eight broken tackles. Those kinds of numbers are unheard of against a Patriots defense under Bill Belichick. The fun didn’t stop there, though. Over the next four games, Hunt averaged 115 rushing yards a game and poured in three more touchdowns. The Chiefs’ running back was making Ezekiel Elliott’s rookie season look mediocre.

As with all good things that seem too good to be true, Hunt’s play eventually took a downturn. From Week 6 on he hasn’t cracked 100 yards rushing once and didn’t even amass 100 yards over his past two outings combined. What changed? Let’s take a look.

Big-play randomness

One of the biggest criticism we often see in PFF’s grading of running backs is when a back has the most yards of the week yet doesn’t even finish among the top five highest-graded backs for the week. What gets lost is that usually 75-plus percent of that back’s yardage came on one or two carries and they were consistently unimpressive on the others.

Big runs, though, are very rarely the result of incredibly perfect blocking. Realistically a perfectly blocked play can only get a running back to the safeties or around eight yards downfield. Defensive failures are frequently more to blame for long runs than anything the offense did. Whether that’s bad angles from safeties, or poor gap control up front, there is a decided randomness to explosive runs that offenses can’t control.

Hunt is a great example of this. He had runs of 50-plus yards each of the first three weeks. Those are obviously going to inflate his raw totals and as noted above, aren’t necessarily sustainable all on his own. There have been so few backs throughout history who have been able to consistently generate those explosive plays that it can be worthwhile to eliminate them altogether when statistically evaluating a running back. Runs that get zero or negative yards can be taken out as well as these are often plays where the running back has no chance of overcoming his run blocking. When that’s done, Hunt still has the second-highest yards per carry of any back with at least 100 carries (Todd Gurley is first).

Line play

One of the single most difficult tasks the analysts here at PFF face when evaluating players is trying to separate the work done by a running back on a certain play with the work done by an offensive line. We have a whole section of our grading handbook dedicated to what constitutes a “positive” for a given run. The phrase that often gets thrown around when discussing when to give a positive for a back is “above and beyond.” That is to say, did he do something to generate more yards than were generated by the run blocking alone?

The fact of the matter is, though, that it’s much easier to go above and beyond when those holes are wider, making reads cleaner. When the starting five of LT Eric Fisher, LG Bryan Witzmann, C Mitch Morse, RG Laurent Duvernay-Tardif and RT Mitchell Schwartz were healthy, they graded out as one of the top run-blocking lines in the NFL. One simply can’t expect to maintain that level of play with injuries to positions as crucial to running game success as center and right guard. With Morse and Duvernay-Tardif missing most of the last month and a half, their replacements have predictably struggled. Cameron Erving has the 59th best run-blocking grade of any guard this season, while Fulton is 24th in run blocking among centers.

Yards before contact isn’t a perfect measure for run-blocking success, but comparing between similar schemes it does a good job of showing the respective effectiveness. Below are Kareem Hunt’s numbers with a healthy offensive line and with backups in.

O-Line Status Yards Before Contact Yards After Contact Broken Tackle per Carry
Healthy 2.8 4 0.28
Banged up 1.7 2.9 0.26

More than a yard difference before contact is massive. The yards after contact difference can almost solely be explained away by the before contact difference, as it’s obviously easier to drag a linebacker or safety than a defensive lineman. The good news for Chiefs fans comes in the last column. Despite the poor run blocking, Hunt has been breaking tackles at a nearly identical rate. That suggests heavily that the run blocking has impacted him. With the Chiefs’ offensive line once again healthy there could be another big day for Hunt in the coming weeks.

Mike Renner is a writer for Pro Football Focus and a contributor to The Washington Post’s NFL coverage.

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