In 2016, Florida State cornerback Tarvarus McFadden was regarded as one of the best defensive players in college football.

In 2018, he wasn’t among the 129 defensive players selected in the 256-man NFL draft.

What happened?

“I honestly don’t know,” said McFadden, who signed a free-agent contract with the 49ers after he wasn’t among the 29 cornerbacks picked.

On Thursday, five days after he dejectedly left his parents’ home in Fort Lauderdale, Fla., near the end of the draft, McFadden pledged to make the best of a situation he didn’t expect to endure.

As a sophomore in 2016, McFadden tied for the NCAA lead with eight interceptions and was one of five finalists for the Bronko Nagurski Trophy, which is given to the nation’s top defensive player.

His performance dipped last year, but the biggest reason McFadden went undrafted had nothing to do with what he did in his college career. At the NFL combine, McFadden ran the 40-yard dash in 4.67 seconds — the third-slowest time among the 57 defensive backs who ran. He posted a 4.58 at his pro day, but he was still left behind by a league that covets speed at his position.

McFadden pointed to his college resume — he was a second-team All-ACC pick last year despite not having an interception — and said too much emphasis is placed on a stopwatch.

“If you put on the film, I’ve never been run right by,” McFadden said. “I’ve given up some plays, but name a corner who hasn’t. I honestly don’t feel like the 40 should make or break these players in the draft.”

With the 49ers, the only team that hosted him for a pre-draft visit, McFadden appears to have a shot at making the 53-man roster. The 49ers value height and length at the position — their projected starters are Ahkello Witherspoon (6-foot-2) and Richard Sherman (6-3) — and McFadden is 6-2 and has 32½-inch arms.

The 49ers reportedly gave McFadden a $20,000 signing bonus and $70,000 guaranteed, which is among the most given to an undrafted player this year. However, McFadden said the fit — not the finances — influenced his decision after several teams, including the Steelers and Dolphins, reached out after the draft.

“Actually, money has nothing to do with it,” McFadden said. “I feel like I can come in and play in this scheme right away. And I’ve got somebody in Richard Sherman to learn from.”

Sherman also can provide inspiration. Like McFadden, he entered the NFL with plenty to prove after an unimpressive 40 (4.56 seconds) led to him slipping to the fifth round in 2011.

Still, speed matters to the 49ers, and McFadden will have to compensate for his lack of wheels.

In the third round, the 49ers selected Southern Miss defensive back Tarvarius Moore, who has a modest college resume and faced lesser competition than McFadden. However, Moore shot up draft boards after running a blistering 40 (4.32) at his pro day.

“You have to be able to run to play (cornerback) in this league,” general manager John Lynch said after drafting Moore, “and he can flat out run.”

On Saturday, even before the draft ended, McFadden left his parents’ house and went to his home about 10 minutes away to be alone during what he said was an “emotional” time.

He since has replaced his sorrow with a bit of swagger as he looks ahead to an NFL career that hasn’t started the way he expected.

“I ran what I ran,” McFadden said, “and people think what they think. But I know what I can do and I just hope to show everybody.”

Eric Branch is a San Francisco Chronicle staff writer. Email: ebranch@sfchronicle.com Twitter: @Eric_Branch