One of the keys to the Detroit Lions' defense stifling the Minnesota Vikings offense the way it did on Sunday night was the performance of cornerback Amik Robertson. Tasked with covering wide receiver Justin Jefferson most of the game (35 of Jefferson's 43 routes, according to Next Gen Stats), the Vikings stud wide receiver had three catches for 54 yards in the game.
Next Gen Stats credited all of that production to happening in Robertson's coverage, while Pro Football Focus gave Jefferson two catches for 48 yards on six targets while being covered by Robertson. In any case, it was a good performance by Robertson and just what the Lions needed from him. Jefferson has been a noted Lions' killer, and that he only had seven targets on Sam Darnold's 41 pass attempts (17.1 percent target share) is a testament to Robertson's sticky coverage.
PFF grade diminishes Amik Robertson's performance against Justin Jefferson
When PFF released their grades for Sunday night's game, it felt certain Robertson would be one of the highest-graded Lions' defensive players.
Robertson is the 11th-best overall graded cornerback by PFF over three games since moving outside to replace Carlton Davis (76.6 overall grade). But his overall grade for Week 18 was just 61.4 (11th among Lions' defenders who played at least 20 snaps in the game) and his 60.4 coverage grade was a step worse. A 60.4 coverage grade would outside the top-85 among cornerbacks for the season as a whole.
Robertson, and the Lions' pass coverage in general, benefitted from Vikings quarterback Sam Darnold playing so poorly with a lot of inexplicably errant throws as Aaron Glenn's game plan had him flustered from the start. PFF grading accounts for things like that (bad throws to open pass catchers, etc.), which can then demerit how they grade coverage beyond the raw numbers someone allowed. Still, with their grades in general, it's fair to wonder what PFF graders are looking at.
The eye test says Robertson was very good against Jefferson on a big stage Sunday night. Most of the numbers say it too, and a PFF grade that accounts for how awful the opposing quarterback was on that same big stage can't diminish what Robertson did when the Lions needed it the most against one of the best wide receivers in the NFL.