SANTA CLARA, Calif. -- San Francisco 49ers left tackle Trent Williams was rarely challenged during training camp. Sure, someone occasionally slipped past him but more often than not, Williams won his individual matchup.

Then, on Aug. 25, defensive end Nick Bosa made his long-awaited return to one-on-one pass rush and drills after missing most of the 2020 season with a torn ACL in his left knee. For Williams, business picked up in a hurry.

"Very few people come back from a major injury and are better than they were when they left and I played Nick before he left and I played him now and he's better," Williams said. "He definitely got stronger, you can definitely feel his play strength, you can feel that off the bat. But honestly, I think he is just such a smart guy and being around the game and studying the game, I think his mind always stays sharp. I feel like he came back with a recipe of moves just for me."

In a year when several prominent players will return from injury -- Cowboys quarterback Dak Prescott, Giants running back Saquon Barkley and Panthers running back Christian McCaffrey, to name a few -- Bosa's return on Sunday against the Detroit Lions is every bit as important to the 49ers.

Following a methodical rehab from the knee injury Sept. 20, 2020, Bosa appears poised to bounce back with a vengeance. He arrived at camp leaner after changing up his diet (more green juice and raw vegetables), and said he weighs around 260 pounds after playing at 263-265 in 2019. The hope is to add an extra half step that will turn more of the 70 quarterback hits or hurries Pro Football Focus credited him with as a rookie into sacks.

"It's just something I like to do, just keep improving myself," Bosa said. "It's my job to take care of my body so I may as well use every resource and thing I can do."

On a roster with no shortage of talent, it's possible Williams is more dominant, linebacker Fred Warner more irreplaceable and tight end George Kittle more versatile. Arguments can be made for all as the Niners' best player. But nobody is more transformational than Bosa.

After being picked No. 2 overall in 2019, Bosa took the 49ers' defense to another level.

In the 17 full regular-season games Bosa played in 2019 plus the first week of last year, San Francisco was sixth in the league in sacks (50) and sacks per drop back (7.7%) while blitzing just 20.1% of the time, tied for fifth lowest in the league. The 2019 Niners finished second in the NFL in defensive DVOA, according to Football Outsiders.

It was enough to make others who played his position and opponents sit up and take notice.

"He has it all," former All-Pro defensive end Justin Tuck said. "I don't see a weakness in his game. ... But that guy has a motor, he has talent, he has hands, he obviously has the build and he's in a system that allows him to thrive. Without the injury, I think he's on track to be one of those guys we talk about for a long time."

Soon after Bosa's injury, a unit that leaned heavily on its front four to generate pressure suddenly had to rely on then-coordinator Robert Saleh to find creative ways to get after the quarterback.

The result was a more coverage-oriented defense that had its share of success, finishing sixth in defensive DVOA, but lacked the game-changing pass rush that it had been built on. For the (most of) 15 games the Niners didn't have Bosa, they dialed up blitzes on 34.1% of drop backs, the eighth most in the NFL but dropped to tied for 21st in sacks (28) and 20th in sacks per drop back (5%).

The Niners missed Bosa and he missed the opportunity to build on his Defensive Rookie of the Year season.

"Nick, at times might have made it look easy his rookie year, but it's never easy," defensive line coach Kris Kocurek said. "It's the most difficult year an NFL player goes through because of the swarm of information, the getting used to the way the NFL works, getting used to the different environment, getting used to different teammates. It's a whirlwind and Nick made it look easy but it wasn't quite as easy as he made it seem on the field. So just getting that second year under his belt where everything is calmed down and now he can really just hone in on some of the small technical aspects of the game and just get more experience under his belt."

Which begs the question of how high Bosa's ceiling can be now that he's back?

Opponents such as Rams offensive tackle Andrew Whitworth still call Bosa one of the top young ends in the league, noting he's not just a good pass-rusher but also a stout run defender.

What sets him apart? That aforementioned power.

"He's just a really strong guy to feel," Whitworth said. "Most rookies don't quite yet know how to use their bodies and use their power. Not that he's necessarily stronger than everybody else, it's just that he really knew how to use his leverage and legs in the run game and everything. I was very impressed with his ability to be able to do that."

For a 49ers team with designs on returning to the postseason and making another Super Bowl run, it's no secret Bosa has to be healthy. And with questions about how their quarterback situation will shake out, a dominant defense would go a long way in buying coach Kyle Shanahan time to figure it all out.

But if Bosa is on the field on a weekly basis, nothing is out of the question: Comeback Player of the Year, All-Pro, even Defensive Player of the Year.

"If he's out there, he's playing, he's always going to do well because he has a really high motor, has great hands," seven-time All-Pro end DeMarcus Ware said. "The sky is the limit for him."