Adrian Martinez will be a rare four-year starting quarterback at Nebraska this fall and yet, for all his experience, he is one of the team’s biggest mysteries.

He was among the best dual-threat quarterbacks in the country as a freshman in 2018 and appeared on Heisman Trophy candidate lists the next spring.

But a sophomore slump set in amid injuries, he seemed to lose a step and committed 13 turnovers in 10 games. It didn’t get better in last year’s pandemic-shortened season.

He continued to struggle hanging onto the ball, and he lost the starter’s job for two games as the Cornhuskers went 3-5.

Martinez faced no serious competition this spring following Luke McCaffrey’s transfer, so how the senior from Fresno, California, plays this fall will largely determine whether the Huskers can win more than five games for the first time in coach Scott Frost’s four seasons.

“There’s been a lot of ups and downs for sure over my career here and I just want to leave it all out there — and not just for me,” Martinez said.

“I think it’s a prove-it year for us, as a team. There’s a lot we’re capable of. That doesn’t mean it’s going to be easy. You have to work for it, prove it to each other and prove it to this state and everybody else.”

The Huskers, who play their spring game Saturday, have made their biggest upgrades at receiver even though 2020 leader Wan’Dale Robinson transferred.

Samori Toure, an FCS All-American at Montana in 2019, joined the team as a graduate transfer, and Omar Manning, the top junior college receiver two years ago, is having an impressive spring after sitting out most of last season with an injury.

Toure and Manning give the Huskers a chance to stretch the field, something they struggled to do under Frost and offensive coordinator Matt Lubick last year.

“I feel confident in what Frost and Lubick are doing to mix it up and give us more opportunities,” Martinez said.

Beyond delivering the ball to his receivers, quarterbacks coach Mario Verduzco said, there’s one point of emphasis for Martinez.

“No more fricking turnovers. That’s it,” Verduzco said. “You have to take care of the damn ball, seriously.”

Martinez, who started six games and played one series in a seventh, lost five of seven fumbles and threw three interceptions.