When Tom Brady fires a game-winning touchdown pass, it can seem as fated an outcome as there is in football.

But even Brady cannot orchestrate an entire offense by himself against a generation of N.F.L. defenses that grew up dissecting his tendencies. The Tampa Bay Buccaneers rank second in the league in scoring, in large part because Byron Leftwich, their offensive coordinator, adapts the offense to the playmakers who revolve around Brady, their star quarterback.

This season, with Covid-19, injuries and other unusual circumstances threatening Tampa Bay’s season, Leftwich has altered his play calls to get the most out of a Frankenstein’s roster.

When the Bucs needed a last-minute drive to beat the Jets in early January, in a game that receiver Antonio Brown unexpectedly and dramatically left in the third quarter, Leftwich dialed up routes for a replacement, Cyril Grayson, a speedy recent promotion from the practice squad. Grayson caught three short passes on the final drive, and when the Jets’ defense sat on quick throws in the closing moments, Leftwich called in a sideline shot that went 33 yards for the score — just Grayson’s 10th catch of the season.

In a league where teams covet plug-and-play diagrams, Leftwich prefers bespoke schemes designed to wrong-foot the defense and options that use the breadth of Brady’s experience. Even if that means Brady shakes him off from time to time, as happened in the season opener, against the Dallas Cowboys, when on the game-winning drive Brady called a 24-yard shot to receiver Chris Godwin.

“He’s been in every situation,” Leftwich said in a phone interview last month. “If there’s an opportunity where he sees something I can’t because he’s on the field, hey man, let’s get to it.”

The approach was a boon for last season’s Buccaneers, whose lineup melded the Pro Bowl receivers Godwin and Mike Evans with free agents Brady had lobbied for, including tight end Rob Gronkowski and the since-released Brown, on the way to a championship.

This season, Leftwich’s adaptability has been even more essential, as the team has returned to being a top-three scoring offense despite Godwin’s season-ending anterior cruciate ligament tear in Week 14 and Brown’s surprise midgame exit. Evans and running back Leonard Fournette have also missed games, though both are expected to play in the postseason.

“It’s not just, ‘OK, you’re going to run my stuff and we’ll do it my way,’” Leftwich said. “We’re going to do what we need to do for our group, as a group, to play well.”

Leftwich, a nine-year N.F.L. quarterback, is, at 41, younger than Brady, 44. He is scheduled to interview for the Jacksonville Jaguars’ head coaching job, a role that last summer went to an untested and since-fired college coach. For now, his tailoring of the offense — and his understanding of its centerpiece — gives the Buccaneers a chance to repeat as champions despite the attrition.

Leftwich says that a play is only as good as the comfort of the quarterback running it, and he often calls Brady late in the evenings to vet designs and adjustments

“When you work together for a long period of time, you begin to see the game very similar,” Brady said before the Super Bowl win. “When he’s watching film, he thinks, ‘Oh, this is what Tom would like,’ and vice versa.”

Leftwich said: “You can’t call plays for a guy unless you know a guy. You can’t.”

Leftwich is perhaps most remembered for one of college football’s enduring displays of mettle. In the first quarter of a November 2002 game, during Leftwich’s last season at Marshall University, an Akron linebacker charged into his planted left leg, breaking his tibia. He went to a hospital to have the leg set and returned to lead a pair of scoring drives, during which his offensive linemen hoisted him between plays and carried him to the huddle.

Playing the next game — against Ben Roethlisberger and Miami of Ohio — was out of the question, so he spent the week poring over film and creating a game plan with his backup, Stan Hill. Marshall won the shootout, 36-34.

As Leftwich prepared for the N.F.L. draft, scouts lauded his arm strength and toughness. But he said his true talent was intuiting his opponents’ patterns and finding plays that scrambled them.

After the Jaguars drafted him with the seventh overall pick in 2003, an accumulation of injuries over time turned him from a would-be franchise quarterback to an esteemed backup. As he bounced from roster to roster — Atlanta, Pittsburgh, Tampa Bay — Leftwich mentored younger quarterbacks, talked coverages with his coaches and collected every scrap of football intel he could, rotating between tables in the team cafeteria so he could sit with receivers one day and defensive linemen the next.

“If I had something he disagreed with, we had to go back and find it on film,” said Ken Anderson, Leftwich’s position coach in Jacksonville and Pittsburgh, “because he wanted to know everything.” He recalled that Leftwich even prepared his own notes for their midweek meetings.

Knowledge is proprietary in the N.F.L. It can help a backup unseat a starter, but Leftwich did not care about hiding what he knew. When he was benched in favor of younger prospects a few games into his 2009 season with the Buccaneers, he made space in his daily routine for tutoring his replacements in the nuances of presnap reads.

“He would take them through all the checks at the line,” said Tim Holt, an offensive assistant on that Buccaneers team. “They’d have equipment guys line up trash cans after practice, and he’d say: ‘All right, we’re checking to this. Which trash can do you have to hit?’ He was so good with the visual part of the game, and those guys needed that.”

In 2016, four years after Leftwich retired as a player, Bruce Arians, then the Arizona Cardinals’ head coach, hired him to mentor the team’s young quarterbacks as part of a fellowship the coach had started to give nonwhite former players a start in coaching. Leftwich rose quickly, first as quarterbacks coach, then as interim offensive coordinator.

When the Buccaneers hired Arians as head coach in 2019, he snatched up his protégé and gave him the offense, knowing it was in good hands.

“He hasn’t been to one of my meetings in three years,” Leftwich said.

Black people remain underrepresented in the N.F.L. coaching ranks. While 69 percent of players are people of color, only 35 percent of coaches are. The league has created new initiatives to try to bridge the gap, teaming with the Fritz Pollard Alliance to surface head coaching candidates of color and expanding its Rooney Rule to require, among other things, an in-person interview with a minority candidate for any head coach or general manager opening.

But some candidates are not well hidden. Last season’s Super Bowl featured two teams that were led by offensive coordinators who are Black — Leftwich and Kansas City’s Eric Bieniemy — and neither was hired in the last off-season to fill a head coaching vacancy. Leftwich seems poised to make the jump, having also drawn interest from the Chicago Bears after the team fired Matt Nagy this week.

For now, Leftwich has more pressing concerns: getting back to the title game with a changing mix of stars and fill-ins. “You’ll have to ask me that when we get to the off-season,” he said of the head coach talk. “I’ve got a good group here, and that’s my job. My job is to know who my players are.”