Three years ago this week, Austin Ekeler entered the Chargers' preseason finale against the San Francisco 49ers knowing that a roster spot depended on his performance.

The undrafted rookie running back from Western State wore No. 3, an unassuming number given to the longshots. What transpired that night in Santa Clara was the beginning of NFL stardom for the ultimate underdog.

"I just remember the importance of that game, especially for the undrafted guys or people [who] may be on the bubble," Ekeler said. "… Just going into that game, just remembering, 'Hey, I studied all my notes. I studied everything, I'm ready to play. Now, it's just go out there and give 100 percent effort and leave it on the field.'"

Ekeler rushed eight times for 50 yards and caught three passes for 58 yards, while playing 44 percent of the special teams snaps. He took full advantage of what he said were those most reps he received that entire camp.

Chargers offensive coordinator Shane Steichen remembers that game well. He was the team's quarterbacks coach in 2017 and has seen Ekeler develop into one of the game's top backs, who's now a leader on the 2020 offense.

"He grinded that," Steichen said. "He knew his opportunity coming as a free agent, he had to do what he had to do. And for him to grow into what he's done is very impressive."

Ekeler caught 92 passes last year – second among running backs to only Carolina's Christian McCaffrey's 116. What's remarkable about that is this: McCaffrey was on the field for 440 more offensive snaps than Ekeler.

Efficiency has been his calling card. Ekeler led the league last season in catch percentage (85.2) among those who received over 50 targets. He can line up anywhere on the field and is regarded as one of the most versatile offensive weapons in football.

All of this is a reminder of how thin a margin it is to make an NFL roster. Had the 2017 version of Ekeler been dropped into the same situation in 2020, he said he's not sure he would make the team.

Instead, he's morphed into a star at the position. Had you told Ekeler that as he was running out of the tunnel of Levi's Stadium in August 2017, this would be the response:

"He would say, 'Man, really? I got a lot of work to do. I better step up.'

"That's kind of been my mindset, is just progress," Ekeler continued. "Do better than I did as far as efficiency and just helping the team than I did last year."