SANTA CLARA, Calif. -- To understand why nobody in his orbit is surprised that Brock Purdy has quickly ascended from the final pick in the 2022 NFL draft to the starting quarterback of the San Francisco 49ers, you have to know two stories: the one about mono, and the other about the saguaro cactus.

The tales are separate but linked in that they were the biggest obstacles in Purdy's early football career. He contracted mononucleosis entering his junior year of high school in 2016 and was on the losing end of a hand fight with a cactus playing paintball with his teammates and coaches the following year.

Those events didn't completely prevent colleges from noticing Purdy, but they made it difficult for him to get scholarship offers, despite a prolific high school career. That is until the NCAA, for the first time, instituted an early signing day in December. That created a frenetic late market for Purdy before the traditional February signing period, as coaches who didn't sign a quarterback early flocked to him to prevent being shut out at the position.

Purdy was arguably the most desirable quarterback in the country between Dec. 2017 and Feb. 2018, with offers from Boise State, Alabama, Illinois and Texas A&M before choosing Iowa State. It was the first time he had quickly jumped from something of an afterthought to center stage.

It also set him on a path to where he is now, preparing to start Sunday for the 8-4 49ers against the Tampa Bay Buccaneers and legendary quarterback Tom Brady (4:25 p.m. ET, Levi's Stadium, Fox), becoming the first 'Mr. Irrelevant' (the final pick in the NFL draft) to start a regular-season game at quarterback.

"I think there's always been an edge to myself," said Purdy, the ninth quarterback picked in the 2022 draft. "I've always believed that I don't care what slot, what round, what pick that I get picked or if I was undrafted, my whole thing was I just want to go out and prove to myself that I can play at this level. And so that's always been my mentality."

Purdy's rise to 49ers' starting quarterback has also been the result of unfortunate circumstances, namely injuries to quarterbacks Trey Lance and Jimmy Garoppolo. But his relentless work habits have led him to this moment.

"He doesn't have to change much," coach Kyle Shanahan said. "He had to prepare a ton. It's real hard to do that week in and week out ... I couldn't imagine studying all week for a test and then not being allowed to take the test. Do it a few weeks in a row and some guys eventually roll the dice and they're like, 'all right, it's not happening' and then the first quarter it happens and then they can't handle it.

"Brock was ready."

AS THE HEAD varsity football coach at Perry (Arizona) High School, Preston Jones was aware of Purdy from his exploits on the freshman team before working in a quarterback timeshare as a sophomore. He was also the backup punt returner, and when Jones would have Purdy practice fielding punts, his job was to throw it back.

Jones would stand 35 to 40 yards away, with a hand near his ear or next to his hip, and ask Purdy to hit either target. According to Jones, nearly every throw would hit within six inches of Jones' hand.

Purdy was the unquestioned starter entering his junior year until he contracted mono about two weeks before the season. He lost 20 pounds and had zero physical activity for six weeks. Passes that used to hum out of his hand floated and wobbled.

When Purdy returned four weeks into the season, Jones planned to ease him in as part of a rotation. Purdy, nowhere near back to full strength, went in on the second series against O'Connor High and never exited, going 25-of-28 for 361 yards and five touchdown passes while running for another 45 yards on 10 carries.

"He was throwing these rainbow bloopers because he had nothing in the tank," Jones said. "He had no strength but he was the most accurate guy I've ever seen."

Purdy continued to pile up numbers, raising Perry from perennial playoff participant to legitimate state championship contender, but his recruitment didn't take off because of the floating, wobbly passes.

During the spring football period prior to his senior season, Purdy joined his fellow seniors and coaches on a retreat to play paintball. In a battle of seniors versus coaches, Purdy found what seemed to be a good hiding spot behind a cactus.

Upon taking evasive maneuvers, Purdy put his left hand up and a cactus spine went directly into it. He ended up in the emergency room and had to have the spine surgically removed. The injury cost him precious time on the spring ball circuit that could have helped with recruiting.

By the time his senior season rolled around, Purdy was finally back to full strength. His throws were up to normal velocity and he regained the weight he'd lost with mono.

Purdy averaged 314.6 passing yards and 72.6 rushing yards per game to go with 67 total passing and rushing touchdowns, leading Perry to within eight points of a state title.

"He was kind of like an old man in a kid's body," Jones said. "He kind of took it like he was playing in the NFL. He was extremely serious in his preparation."

FOR IOWA STATE coach Matt Campbell, the normal opening recruiting call lasts roughly 10 minutes. When Campbell talked to Purdy for the first time, the two chatted for about an hour.

When he ended the call, Campbell couldn't believe Purdy, who was in the throes of a suddenly intense recruiting battle, was so humble and mature. Pairing that with high school tape that reminded Campbell of Baker Mayfield only made Purdy more appealing.

Iowa State didn't have the glitz of some of the other schools recruiting him, but that was part of its appeal to Purdy, who viewed it as a place where he could build something.

Any doubt that Purdy could take the Cyclones to new heights was erased in his first extended playing time at Oklahoma State as a true freshman in 2018, when Purdy replaced starter Zeb Noland in the first quarter. After throwing an earlier touchdown pass, Purdy pulled the ball on a zone read and raced 29 yards for a score, ending with a mini high step as he crossed the goal line.

"At that moment, I'm like, 'Oh, buddy, everybody better get ready,'" Campbell said. "This guy's got a chance to be really special. And from that point forward, he was as big of a transformational figure in the history of Iowa State football as anybody that's ever played here."

And much like after his first post-mono high school performance, Purdy never again relinquished the job at Iowa State. He started 46 games and broke or tied 32 school records while winning more games than any Cyclones quarterback ever. He led Iowa State to its first-ever Big 12 championship game as a junior in 2020, a season in which it finished 9-3 and defeated Oregon in the Fiesta Bowl.

"I think his greatest toughness is his mental toughness," Campbell said. "This was a program that really had never had consistent success. ... From Day 1, I feel like this community and the people around this community put Brock on the pedestal. ... And I think how he handled himself through the journey of those highs and lows [was] really powerful."

LEADING UP TO the NFL draft in April, Purdy believed he could be picked as early as the fourth round or potentially go undrafted. He had all the intangibles, but there were questions about his size (6-foot-1, 220 pounds) and arm strength.

Those questions pushed Purdy to the last pick in the draft, a selection that comes with the "Mr. Irrelevant" title. The Niners loved Purdy's extensive college experience and were inundated with endorsements about his work ethic and moxie. They made the pick, with general manager John Lynch immediately noting Purdy was "relevant to us."

Each year, Mr. Irrelevant is welcomed to Newport Beach, California, for a week of activities he helps choose. Purdy wasn't too familiar with all the title entailed but, after some initial reticence, embraced the opportunity.

His week included a banquet -- where he was awarded the "Lowsman Trophy" instead of the Heisman -- surfing and sailing lessons, a trip to Knott's Berry Farm and comfort-food meals like fried chicken. The tradition, started by founder Paul Salata, a former NFL receiver, is meant to be celebratory and fun. But Purdy was once again a quick study, getting up on his surfboard and riding a wave and winning a race in his first sailing attempt.

More than anything, he earned a bunch of new fans in Melanie Fitch -- Salata's daughter and the CEO of Irrelevant Week -- and the many volunteers who make the week happen. There have been other Mr. Irrelevants, such as Bucs kicker Ryan Succop and New York Giants linebacker Tae Crowder, who have gone on to successful careers.

But there's never been a Mr. Irrelevant who suddenly became extremely relevant like Purdy.

"This is the story now," Fitch said. "He's the last guy drafted in the draft and he's playing, he's going to start. That's a long journey in the NFL because there's a lot of really good players that never do start or never really get to get in the game. We just want him to stay healthy, play well, stay poised and, well, be relevant."

play

Adam Schefter talks about why there is confidence in the 49ers locker room about Brock Purdy.

AFTER THE 49ERS acquired running back Christian McCaffrey on Oct. 20, McCaffrey went through a crash course on the offense. Among his tutors were assistant coaches like Anthony Lynn and Bobby Turner. Perhaps the most unlikely resource, however, was Purdy.

Coming from the Carolina Panthers, McCaffrey knew little about Purdy, but it was the rookie quarterback who stepped up to help McCaffrey learn the offense. On Saturday nights before McCaffrey's first couple of games, the pair would sit down and recite the play sheet. It gave McCaffrey a chance to commit them to memory and helped Purdy practice verbalizing the plays like he would in a huddle.

They even went out to the field one Friday and did a walkthrough together.

"The first couple days I figured out a lot about him and his mentality and his work ethic and wanting to be great and wanting to help out," McCaffrey said. "He jumped at the opportunity and I really appreciative for it."

Similar stories popped up in San Francisco's locker room this week. Left tackle Trent Williams and tight end George Kittle compared Purdy to a 15-year veteran, noting his willingness to take control of a huddle and tell an unnamed teammate to be quiet when he's trying to call a play.

Linebacker Fred Warner and other defenders have raved about Purdy's willingness to take chances against their defense when running the scout team, with Warner citing the same "competitive excellence" Campbell saw in Purdy's high school tape.

Don't expect Purdy to put up the big numbers he did in high school and college. The 49ers won't ask him to. He has plenty of help, meaning his job is to take care of the ball and get it to the playmakers.

And Purdy hasn't deviated from what got him here. On road trips and other select nights, the Niners offensive linemen and tight ends get together for low-stakes poker games, buy-ins never exceeding $100 a person. When Purdy plays, he doesn't let being relatively new to poker stop him from being aggressive. Guard Daniel Brunskill also knows better than to get his hopes up about Purdy joining when he extends the invite.

"He prepares all the time," Brunskill said. "Brock says 'No, I gotta go study.'"

After all, in staking their Super Bowl hopes on Purdy, the 49ers are placing the biggest bet of all.