Koski grew up in Danville, California and attended San Ramon Valley High School, where he played basketball and football and ran track.
[2] As a redshirt senior he caught 42 passes for 868 yards and eight touchdowns and was named first-team All-Big Sky.
[5] He was waived on September 4, 2020, during final roster cuts, and was subsequently signed to the team's practice squad one day later.
[10] He made his NFL debut and returned one punt for seven yards in a 16–28 loss to the Tennessee Titans on November 7, 2021.
Koski won Super Bowl LVI as a member of the Rams backup players when they defeated the Cincinnati Bengals.