The grade came back a season ago and all at once it told Aaron Donald everything he kind of already knew. He was contemplating leaving Pittsburgh, his college and childhood home, before his final season of college for the NFL.

He thought he might be ready. The pros told him not quite. If he had left early, he would be a third-day pick, somewhere between the fourth and seventh rounds. He was a good player and an undersized player, not a great player. Being competent in college is one thing. There are a lot of nice college players.

Aaron Donald's attention to detail helped him become one of college football's top defenders in 2013. Charles LeClaire/USA TODAY Sports

Being a dominant one is different. Being a pro, something else entirely.

“I thought I was a better player but making the choice, I felt I wasn’t 100 percent ready for the next level. I think I had not dominated enough on the college level,” Donald told ESPN.com last week. “Even though I had success my sophomore year and my junior year I felt like I didn’t have that year where I felt comfortable that I accomplished what I wanted to accomplish in college, and now I’m ready to move on.

“My senior year I felt I put a lot more time into the offseason to make a lot more happen. Going out my senior year, I felt like I did everything I wanted to do and more. I felt like I dominated and I feel comfortable going to the next level and that I’m ready.”

The grade and the subsequent decision turned Donald from that decent late-round player into the game-changing defensive lineman in college football. The one whose statistics compared favorably to Ndamukong Suh’s last year at Nebraska and who transformed from a final-day prospect into a first-day one.

He swept essentially every major defensive award he was up for: The Nagurski, Bednarik, Outland and Lombardi Awards. He drew comparisons, even at 6-foot, 285 pounds, to both Suh and Geno Atkins, two of the best defensive tackles in the NFL.

Donald, despite his size, became a marketable and coveted prospect for NFL franchises – even one the Lions could consider at No. 10 since their top six defensive tackles are all due to be unrestricted free agents after the 2014 season. Declining to pick up Nick Fairley’s fifth-year contract option opened up Detroit to the possibility of taking their third defensive tackle in the first round since 2010.

Doing so could turn defensive tackle into the same position for general manager Martin Mayhew that wide receiver was for his predecessor, Matt Millen, and could link the Lions with drafting tackles in the first round in the 2010s like wide receivers were for Detroit in the 2000s. Except the Lions need to upgrade a defense built on a pressure-and-chaos causing line.

In one season, Donald solidified himself as a player who could improve the Lions' defense – and most defenses in the NFL.

Some of the shift had to do with scheme and familiarity. He spent his junior season adjusting to being a 4-3 defensive tackle after spending his first two seasons in a 3-4 as a nose tackle and defensive end. Returning for his final season allowed him to cause havoc across every offensive line he faced, with slide protections and double- and triple-teams coming his way every play.

He won all those awards anyway.

“He understands the game so well he could put himself in position,” Pittsburgh’s defensive line coach, Inoke Breckterfield, said. “He knows what play is coming off of film study. He can narrow it down to two or three plays and off the first step, he knows what play he’s getting.

“I think film study has really helped his game grow in terms of what techniques would be needed here or what are his tendencies on that.”

Donald’s studying changed. He knew to get from late-round prospect to the best defensive player in college football, he had to know everything about himself and his opponent.

So every Saturday after he finished being beaten up and chipped and doubled on the Panthers’ defense, he lugged himself up to the team’s defensive line room. He popped in a DVD of the game he just played in and watched every play at least twice and sometimes four or five times.

Coaches never said anything to him about it – they weren’t going to tell him no – but they would smile at him when they saw him either leaving the facility late at night or the next morning. They understood that he, too, understood.

“I don’t care if it was 2 o’clock in the morning after a night game,” Donald said. “I had to break down the film by myself before I watched it with the team. I wanted to see everything I did wrong and did right or I wouldn’t be able to sleep.

“After games, you think about the play you missed. I had to see it.”

What he saw was an ever-growing collection of pass-rush and run-stopping moves he added throughout the course of his career. He saw how opponents would try to stifle him and then he would start watching his next opponent to both learn their plays and to get a feel for what they might do to him.

By Saturday, he usually knew almost every play an opponent was going to try and run at him, so he could glance at an opposing offensive line or backfield and narrow things down before the ball was snapped.

It confirmed everything Breckterfield initially saw when he started coaching Donald.

“I would tell anyone who wanted to listen there was something special about that kid,” Breckterfield said. “I said, but he’s 6-foot tall, 6-1, that’s what he is, but I knew he was a special one. I knew he was a special player.”

On the college level, he was. He’ll need to learn even more to reach that on the professional level. But what he did last season will at least give him a chance.