The 6-foot-2, 196-pounder from King High School in Seattle led the Knights to an 11-1 record last season as a senior and completed 196-of-304 passes for 2,997 yards and 46 touchdowns. Green also rushed 80 times for 432 yards and six TDs.
“Billy is a great athlete, football player and fine young man,” Mendenhall said. “We are excited to have him join the program.”
Green, a two-time Cascade Conference Offensive Most Valuable Player, earned AP All-State first-team selections in 2011 and 2012.
As a junior, Green passed for 2,297 yards and 38 touchdowns and rushed for 157 rushing yards and two touchdowns.
Green was also recruited by Notre Dame, Oregon State, UCLA, Utah, Washington and Washington State.