On Monday—as he typically does—Detroit Lions coach Dan Campbell ran through a list of players he believed stood out in a positive way in the previous game. When it came to Detroit’s game against the Green Bay Packers, Campbell listed nine players: Tim Patrick, Jared Goff, Sam LaPorta, Dan Skipper, Pat O’Connor, Za’Darius Smith, Ezekiel Turner, Terrion Arnold, and Khalil Dorsey. However, it was his comments on Arnold—the Lions’ first-round rookie cornerback—that stood out the most.

“I thought that was Arnold’s best game of the season,” Campbell said.

Statistically, it’s hard to pinpoint why Arnold’s performance was so good. He finished with three tackles, a PFF grade of 60.5, allowed two catches on two targets for 9 yards, and was tagged with another pass interference penalty—his seventh of the season (NFL high).

However, Campbell noted how the team’s man coverage was outstanding against Green Bay.

“We were really sticky in coverage,” Campbell said. “There were a couple of things that got us in coverage, but overall, our man-to-man coverage was really good, we were all over those guys.”

There is some evidence of this statistically. According to NFL Pro, the Lions allowed just 2.9 yards of separation per pass target, which was tied for the third-best mark of the week (average is about 3.7).

Like most rookies, Arnold has had an up-and-down first season. Given he’s asked to play such a high percentage of man coverage—mostly a tougher ask—it should not be surprising that it hasn’t been a perfect rookie season.

But Campbell pointed out that this is the time of year in which rookies either hit the wall—because this is when college seasons end—or they thrive. He pointed to how Amon-Ra St. Brown, Penei Sewell, and Alim McNeill all broke out during the end of their rookie seasons. He believes the same may be happening with Arnold.

“I feel like that’s where Arnold’s at,” Campbell said. “He’s starting to push through this and he’s gaining enough valuable reps, experience, he’s not letting the grind of the season weigh him down and he’s getting better.”

The Lions have not taken it easy on their first-round selection. Per PFF, Arnold has played 716 defensive snaps this season, third among all rookie cornerbacks. His 239 man-coverage snaps are most in the NFL and nearly 100 more than the nearest rookie (Quinyon Mitchell, 147). But despite the tough assignments, Arnold has only allowed 21 catches on 42 targets for 245 yards, one touchdown, two pass breakups and a passer rating of 76.0 while in man coverage.

If Arnold has truly turned a corner, the Lions defense could reach another level down the stretch as they continue to get healthy. Currently, the Lions defense already ranks second in points allowed (18.0 PPG), and their pass defense ranks first in passer rating (76.5), 10th in yards per attempt (6.9), and first in DVOA. If Arnold continues this upward trajectory and the Lions get some defensive players back from injury, look out.