Seahawks backup QB No. 2: Geno Smith
This might seem like I am cheating a bit, but just like with Kitna, Smith started off as a backup in Seattle, of course. Plus, when Smith took starter Russell Wilson's place for three games in 2021, he might have done well enough to change the course of how the franchise would go. Mind you, if Russell Wilson had not reportedly gone to Seahawks chairperson Jody Allen to try to get head coach Pete Carroll and general manager John Schneider fired, maybe Smith still doesn't become the starter.
Smith backed Wilson up for three seasons, from 2019 through 2021. In 2019, he saw zero snaps, but this was common when Wilson was the starter as he played every down of every game from 2012 through 2019. In 2020, Smith saw action in one game, a Seattle blowout of the New York Giants in Week 14. Then in 2021, something unexpected happened; Russell Wilson got hurt.
In Week 5 against the Los Angeles Rams and with Seattle's offense struggling badly, Wilson threw a pass and hurt his finger. Smith came in and played most of the second half and looked in full control of the offense. He had a touchdown pass and an interception, but Seattle was down by so much that Smith had to force a bad throw or two. Smith started the next three games and the team went 1-2, but Smith seemed to not be allowed to do too much.
But Wilson was traded in the offseason of 2022, of course, and Geno Smith became the starter. Whatever he had done in 2021 gave the Seattle coaching staff enough confidence to let Smith be a bit freer in his play. Smith was so efficient during his first year back as a full-time starter since 2014 that he led the NFL in completion percentage and won the Comeback Player of the Year Award.