Shawn Petty played quarterback at Eleanor Roosevelt High School. (James A. Parcell/FOR WASHINGTON POST)

A teenage Shawn Petty would tag along with his father in the Howard University football offices, just because he couldn’t stop learning. They arrived at the Northwest Washington campus together in the early mornings and left late at night, soaking up the knowledge, bringing dinner into the film room so as not to waste precious time.

But Rayford Petty never coached his son in youth football, just in the classroom. Had he done so, Shawn probably would have committed to Howard, where Rayford is the Bison’s defensive coordinator after a five-year stint as the team’s head coach from 2002 to 2006. Shawn — who started at linebacker and quarterback at Eleanor Roosevelt High — instead chose Maryland, where he had a chance to play sooner rather than later on defense. The Terrapins employ a four-linebacker system, and plenty more can play on special teams.

Of course, few could have envisioned the startling turn of events in College Park, with four Maryland quarterbacks sidelined with season-ending injuries. So the true freshman Petty, still wearing the No. 31 given to him as a linebacker, will be the Terrapins’ starting quarterback Saturday against Georgia Tech, the culmination of a dream that seemed too improbable to even attempt.

“Naw, I’m not nervous,” Rayford Petty said this week in a telephone interview. “Just talking with Shawn, he’s excited about the opportunity of a lifetime for him. Something he’s always wanted to do. It’ll cost him his redshirt year, but at the end of the day this is what he always wanted to be. Having an opportunity to play quarterback, not necessarily be the guy. That’s what he’s done all his life and all his life in football.”

During his junior year at Eleanor Roosevelt, Shawn Petty had a guide pin surgically inserted to fix a broken clavicle suffered against Oxon Hill five weeks earlier. Rarely a vocal leader, yet always a source of inspiration for teammates, Petty was cleared the day before the Raiders’ 4A South region semifinal against Suitland. Petty begged to play defense, too, but Coach Tom Green only let his star quarterback line up under center. The result? Three total touchdowns and a 20-14 win.

A three-year starter at Eleanor Roosevelt, the 6-foot-1, 230-pound Petty ran the triple option, averaging around 15 carries per game with a powerful running style and a quick release in the pocket. “He’s a bruiser. He can lay some wood out there,” Maryland center Evan Mulrooney said. “Everyone’s looking forward to seeing how many guys he runs over this weekend.”

That Petty will even line up under center, let alone attempt to bulldoze Georgia Tech defenders, is miraculous enough. A lifelong quarterback — the first day he showed up for the Kettering-Largo-Mitchellville Football Program, Shawn’s father volunteered him as the signal-caller — Petty was a 2011 first-team All-Met selection at linebacker but did not receive a scholarship offer to play quarterback in college.

“I bet he’s blown away, as far as getting an opportunity to do this,” said Sam Durant, Petty’s coach with the KLM Steelers. “I’m pretty sure he didn’t think he’d get an opportunity to play quarterback at Maryland. I think he’s really blown away as far as this. He always smiles, so I’m pretty sure he’s smiling and grinning from ear to ear.”

That smile, Maryland offensive coordinator Mike Locksley said, has been its widest throughout the week. Before Petty switched positions, becoming Caleb Rowe’s backup in advance of last Saturday’s game against Boston College, Locksley’s interactions with the linebacker had been limited to his play on Maryland’s scout team during practice, yelling at Petty for providing improper coverage.

Now Petty enters meetings with a broad grin, breaking his joviality only to take notes and ask questions. Locksley thinks Petty prepares like a player who has something to prove. Mulrooney agreed, saying Petty has that “quarterback swagger.” They might be right.

“He’s a pleaser. He’s going to do all he can,” Green said. “He keeps everyone calm, never gets too excited about any one thing. If he makes a mistake, he can let an interception or a fumble go. He’ll stay positive no matter what the situation is, which is good. He’s not a vocal guy. Lead-by-example type of guy. He’ll never be the rah-rah and the talk.”

Two weeks ago, Durant brought his Steelers to Byrd Stadium, where they took the field for a game under the lights after the Terrapins beat Wake Forest. Durant ran into a few KLM alumni in College Park, including offensive lineman Peter White and linebacker Kenneth Tate.

But he never saw Petty on the field, as Shawn didn’t dress for Maryland’s 19-14 win over the Demon Deacons. Instead, he walked the sideline that afternoon, wearing black sweatpants and a Terrapins warmup jacket, cheering on the players he would soon join, sooner than he ever expected.