Costello struggled during an injury-plagued 2019 season. The 6-foot-5, 222-pound pivot completed 61.1 percent of his passes, finishing with 1,038 yards passing and six touchdowns. That stat line followed a highly successful 2018 campaign that saw him throw for 3,540 yards and 29 touchdowns during his second year with the Cardinal.
Davis Mills took over for Stanford as Costello battled injuries, throwing for 1,960 yards and 11 touchdowns on the year.
Costello is certain to have suitors across the country. Entering the portal as a graduate transfer, he has immediate eligibility for next season.