One of the most important pieces of Alabama’s No. 1-ranked defense played flag football during his first semester on campus in 2013.

Levi Wallace’s head was in his schoolwork and his heart was 1,500 miles away back then. His dream of one day playing for Nick Saban and the Crimson Tide was getting away from him. “I had a lot going on in my life,” he said, “so I was ready to let football go.”

To scratch that competitive itch, he participated in intramural sports. That is, until his father stepped in.

Walter Wallace didn’t raise his son to settle. When his 22 years were up in the Air Force, he retired and promised himself he would never work for anyone again. “We’re going to do our own thing,” he told his wife, Wendy. And together, they opened laundromats, preschools and a dojo in Tucson, Arizona. Not every start-up would pan out, but the Wallaces were undeterred. Walter would tell his boys, Levi and Lawrence, “Life is available, you have to go out and get it.”

Walter understood why Levi wanted to give up on football. During a visit home for the holidays, Levi saw just how much his father’s battle with ALS had progressed. Walter had lost significant weight and would need a feeding tube soon. Wendy gathered Walter and the boys around for a photo, fearing that they might not get the opportunity again.

When Levi said he wasn’t going to go back to Alabama, that he would stay and take care of them, Walter and Wendy put their foot down. No, he would return to school and Walter would encourage him to give football one last chance.

“Just see how good you are,” Walter told Levi. “You’re a great football player, so you might as well give it a shot and see where things go.”

In January, Levi got up the nerve to make contact with the Alabama football team about a tryout. He was told to come out to practice and see what he could do. Because of scholarship limitations, even a school like Alabama needs extra players for the scout teams -- essentially cannon fodder for practice. Levi would enter a trial by fire, one that made a habit out of turning many walk-ons away within the first year.

Levi was a nobody back then with no expectations. He had exactly zero scholarship offers coming out of Tucson High School, where he played defensive back, receiver and returned kicks. “Maybe Western New Mexico came through,” his former coach, Justin Argraves, recalled, “but that was pretty much it.”

The problem when it came to Levi’s recruitment was two-fold. First, he was woefully undersized and didn’t have eye-popping statistics. He was maybe 140 pounds as a senior, and his 40-yard dash left a lot to be desired. It would take a good hour or so of watching film to see what he was capable of, Argraves explained, and that was about 59 minutes too long for most top-tier programs to spend on any one no-star recruit. Secondly, Levi wasn’t all that interested in impressing other schools.

Walter grew up in Tuscaloosa, Alabama, and always talked about his boy one day playing ball at Alabama. It wasn’t pushed on Levi, but it wasn’t a secret, either. And he figured that if he was going to play anywhere, it might as well be for his father’s beloved Crimson Tide.

“Regardless of whether the University of Arizona or Oregon offered,” Argraves said, “he told me from Day 1 of his sophomore year that he was going to Alabama. That was his goal. He wasn’t going to let anything stop him.”

And once Levi got a foot in the door, you weren’t going to get him out.

Like his father, Levi isn’t prone to self-doubt. He said it took him maybe a week of practice to feel that he had the talent to fit in.

That small frame of his? That would be no problem for Alabama’s nutrition team, which would slowly build up his weight. And those worrisome measurables? Strength and conditioning coach Scott Cochran would maximize those, getting him into the 4.5-second 40-yard dash range.

Linebackers Shaun Dion Hamilton and Anfernee Jennings saw Levi emerge and understood early that he wasn’t your typical walk-on. Star wideout Calvin Ridley arrived on campus a year after Levi tried out and was confused why he was on the scout team to begin with.

“I was like, ‘This guy is really good. I don’t know what we’re doing,’” Ridley said. “But he’s finally getting a chance to show his talent off and he’s playing great. He’s awesome.”

It was a slow build for Wallace, but he has made the most of his opportunity.

He would spend two years on the scout team before earning a scholarship and cracking the depth chart primarily on special teams in 2016. He saw the field as a cornerback sparingly until Marlon Humphrey was injured against Auburn and Levi’s number was called. When Humphrey left early for the NFL draft after the season ended, Wallace got his first real shot. He would beat out younger, more promising prospects like Trevon Diggs, the brother of NFL wideout Stefon Diggs, for a starting job.

He’s held onto that job all season because he’s more than just a good story, too. He has a team-high three interceptions and nine pass break-ups to go along with a pair of sacks. According to Pro Football Focus, he’s allowing an FBS-best 5.1 passer rating when targeted. He said he wasn’t aware Midseason All-American teams existed until the Associated Press and Sports Illustrated named him to their lists.

Now, he’s getting buzz as an honest-to-goodness NFL draft prospect.

“We’ve had a lot of walk-ons through the years that have done a really good job of becoming contributors to the team,” Saban said. “Levi’s probably done it as well as any of them.”

The unfortunate part? His father hasn’t been around to see it.

On April 18, 2014, Walter passed away at the age of 59 from complications from ALS. It was the night before Levi’s first spring game at Alabama.

Walter made Wendy promise not to tell Levi if he were to die before the game, and despite warning close friends and relatives to keep the news quiet, someone posted about it on Facebook. Around 6 o’clock the next morning, Levi called. He’d seen the post. He asked, “Mom, is it true?” and she was forced to say yes.

“I heard a scream on the other end of the phone and it was the worst feeling ever,” she said.

Somehow, Levi composed himself enough to play in a football game that day. Wendy watched as family and relatives waited with her for the coroner to take Walter’s body away. She can’t remember exactly when she saw Levi first set foot on the field, but she knows precisely what she did afterward. “Hey, Walt, he did it,” she said. “Your boy, he did it.”

“I think about him all the time," Levi said. "Right before I go out onto the field, I look up and thank him for the opportunity, for believing in me."

If they’re being honest, neither Wendy nor Argraves could have predicted this.

There are plenty of walk-ons in college football, but how many become starters, let alone stars of top-ranked programs?

“Did I see it coming? Not really,” Wendy said. "But I knew the determination and the perseverance was there. What I’m most impressed with is the character of the perseverance to get up and say, ‘I can do this,’ because at the end of the day all you have is your character. Are we going to sit around and mope? Or are we going to try? Even if we have failures, are we going to try again? That’s who we tried to raise our children to be.”

Said Argraves: “I’m not going to lie that, ‘Yeah, I projected he would start his senior year,’ because you’re talking about Bama and 98 percent of high school players in this nation couldn’t play for that team. But what didn’t surprise me or the coaching staff or people around here was that’s just Levi, he’s going to go out there and give it his all and he’s not going to let any obstacle or setback get in his way. That’s not in his DNA.”