ALLEN PARK >> If rookie cornerback Terrion Arnold was still playing at Alabama, he’d only have one more game to go — the Crimson Tide will play Michigan in the ReliaQuest Bowl on Dec. 31 to end their season — before being able to give his body a well-deserved rest.

But he’s no longer a student-athlete in Tuscaloosa. He’s in Detroit, a dozen games into his professional career. He’ll have to play seven more times before getting an extended break if all goes to plan, as the Detroit Lions hope to secure the No. 1 seed in the NFC before marching their way to Super Bowl LIX in February.

Some rookies understandably hit a wall at this point in their first seasons. Never before have they had to play 17 games, plus whatever comes in the playoffs. They’ve also never had to see this level of competition on a week-to-week basis; Alabama got a reprieve with FCS program Mercer in November. The NFL, meanwhile, doesn’t let up.

Other rookies begin to flourish and separate themselves from the pack at this juncture. Take receiver Amon-Ra St. Brown, as an example. The former fourth-round pick out of USC had 352 yards through the first 11 games of his career, but he exploded for 560 yards over the final six games of 2021, including a game-winning 11-yard touchdown against the Minnesota Vikings in Week 13 to secure the first win of head coach Dan Campbell’s tenure. Offensive tackle Penei Sewell took his lumps early that season before settling in, too, as did defensive lineman Alim McNeill.

So, what kind of rookie is Arnold going to be?

“What happens with a lot of rookies, especially guys that you’re counting on, unfortunately, some of them start to take a nosedive because this is where their season begins to dip down; it’s over,” Campbell said Monday. “But then the other ones who hang in there, they really start taking flights. What St. Brown did his rookie year, right? He started to take off once we hit November, December. He started to gain strength.

“Sewell did the same thing; Mac did the same thing. I feel like that’s where Arnold’s at.”

Campbell praised Arnold for his performance against the Green Bay Packers last Thursday, calling it the best game of his young career. Arnold was targeted three times in coverage, with one of those being a screen pass thrown in his direction that went for three yards and another being a 6-yard pickup by Christian Watson on a drag route that was ultimately short of the sticks on third down.

The other play directly involving Arnold came near the conclusion of the second quarter, when the cornerback was guarding Watson near the goal line. Watson ran a corner route to the back of the end zone, and Arnold was initially sticky in coverage. The play broke down as the pass rush couldn’t break through, though, and Watson started working back to his quarterback. Arnold, who grabbed Watson and got his head around late, was whistled for pass interference.

It’s the 10th time this season Arnold has picked up a defensive penalty, but that doesn’t tell the whole story. Eight of those infractions came in the season’s first four weeks, with three — a pass interference and two defensive-holding calls — coming against the Seattle Seahawks on Sept. 30.

The only other time Arnold has picked up a penalty since Week 4 was at the Houston Texans in November, when he hit receiver Xavier Hutchinson early on a deep ball 41 yards down the field. Arnold doesn’t have much of a problem with being out of position, but coaches have been trying to instruct him to be less grabby and to get his head around when the ball is in the air.

Pro Football Focus grades aren’t perfect, but they do give a general idea of how a player is performing. From Weeks 1-8, Arnold had an overall defensive grade of 49.5, which ranked No. 112 out of the 121 cornerbacks who had played at least 100 snaps over that stretch.

From Weeks 9-14, Arnold has a grade of 58.0. That’s good for 68th among the 114 cornerbacks who met the 100-snap criteria. Not perfect by any means, but it signals the type of tangible improvement that’s giving Campbell optimism.

“He’s starting to push through this and he’s gaining enough valuable reps (and) experience,” Campbell said of his rookie. “He’s not letting the grind of the season weigh him down, and he’s getting better.”