Colbert made his return to the field the week of the 49ers final preseason game against the Los Angeles Chargers. It was his final audition to land a spot on the roster, and he needed to leave a lasting impression.

On the Chargers second possession of the game, Colbert delivered a punishing hit on running back Kenjon Barner that forced a fumble. If Colbert was truly on the bubble, that play may have been what tipped the scales in his favor.

"He's relentless in his work ethic and his preparation. I love the way he hits. He's a very physical football player," Saleh said. "I don't know if it's a chip as much as it is important, where every play, every rep, every meeting is very, very important. He's very into it. He has something to prove for sure."

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Colbert did his best to treat the morning of final roster cuts just as any other. He worked out at the 49ers team facility, got treatment and passed time by playing video games. Colbert did his best to ignore the various calls and texts from friends looking for updates regarding the safety's future in San Francisco.

As the 1:00 p.m. PT deadline loomed, Colbert took the approach that no news, is good news – more specifically, the best news. His intuition served him well. Colbert's name wasn't among the team's final cuts, meaning he'd defied the odds and earned a spot of the 49ers 53-man roster.

Even though he was at the bottom of the depth chart at safety, his ability as a gunner on punt coverage helped the rookie find the field immediately.

"That's one of the main things I knew they wanted out of me was being a good special teams player," Colbert said. "In college when I wasn't starting at safety, I was doing really well at special teams. I took pride in that. If you're not contributing on the defense or the offense, special teams is the only thing that is going to keep you on the roster. I took great pride in that and took it very seriously."

Just like training camp, key injuries during the regular season thrusted Colbert into action on defense. Ward and Tartt went down with broken forearms in back-to-back weeks. Tartt left just 19 snaps into a Week 9 home game against the Arizona Cardinals, and Colbert was called upon to fill in at free safety. The rookie immediately turned heads while making a diving play to breakup a deep sideline pass intended for Cardinals speedster J.J. Nelson.

"He has the 40 time to do that," head coach Kyle Shanahan said of the rookie. "Lots of guys in the NFL have the 40 time to do it. But, it also goes with instincts. So, you've got to be out there, you've got to play, you've got to learn how to track the ball and watch the quarterback. That was a very good play that he made."

Tartt, who was having a breakout season in his own right, was placed on a season-ending Injured Reserved the following week. In a matter of weeks, Colbert had risen from a third-stringer to San Francisco's starting free safety.

"I'm excited that the coaches put trust in me to start," Colbert said. "Everything happens for a reason. I feel like everything that's happened from camp until now has been preparing me for what's to happen in the future."