Warner (6-3, 236) was the first of two third-round draft picks (70th overall) selected by the 49ers in this year's draft out of Brigham Young. He played in 49 games (42 starts) in four years at BYU and registered 264 tackles, 32.0 tackles for loss, 6.5 sacks, seven interceptions (returning two for touchdowns), five fumble recoveries, three forced fumbles and 13 passes defensed. His seven career interceptions rank second in school history among linebackers. In 2017, he was named a team captain and started all 13 games, notching 87 tackles, nine tackles for loss, one sack, one interception, one forced fumble, one fumble recovery and five passes defensed. As a junior, he started all 13 games and notched 86 tackles, 10.5 tackles for loss, 1.5 sacks, three interceptions (returning one for a touchdown), two forced fumbles and six passes defensed. In 2015, he played in all 13 games (12 starts) and tallied 67 tackles, 11.5 tackles for loss, four sacks, two interceptions, four fumble recoveries and one pass defensed. As a freshman, he played in 10 games (four starts) and registered 24 tackles, one tackle for loss, one interception which was returned for a touchdown and one pass defensed.