Stanford quarterback K.J. Costello has entered the NCAA transfer portal, a source confirmed to 247Sports. Costello, a rising senior, will be classified as a graduate transfer and eligible immediately according to NCAA rules. 

Costello was the starting quarterback for the Cardinal for the latter half of the 2017 season, the entire 2018 season and for five games during the 2019 season as he battled through multiple injuries. His best season came as a sophomore when he threw for 3,540 yards, 29 touchdowns and 11 interceptions for a Cardinal team that finished the campaign 9-4. 

The 2019 season got off to a strong start for Costello when he competed 16 of 20 passes for 152 yards and one touchdown in the first half of a win over Northwestern. But a gruesome helmet-to-helmet hit knocked him out of the game and he was absent in the loss to USC one week later. Junior Davis Mills, a five-star prospect in the Class of 2017, started in his place. He came back in losses to UCF and Oregon but injured his hand against the Ducks and missed the next three games. Costello returned in the win over Arizona on Oct. 26 but was knocked out of the loss to Colorado the following week after another vicious hit which ended his season.

A four-star quarterback and the No. 46 overall player in the class of 2016, Costello will be a hot commodity on the graduate transfer market this offseason. The injury concerns will be difficult to ignore, but he showed during his three seasons with the Cardinal that he has tremendous upside as a pro-style passer.