On the same day senior offensive assistant and tight ends coach Greg Roman was hired to help revamp the running game, the Ravens said goodbye to two assistants from their coaching staff.Offensive line coach Juan Castillo is leaving Baltimore after four seasons to become the offensive line coach and run-game coordinator for the Buffalo Bills, who hired Carolina defensive coordinator Sean McDermott to be their new head coach earlier this week. McDermott is also hiring Ravens secondary coach Leslie Frazier to be his defensive coordinator.Both Castillo and Frazier worked with McDermott in Philadelphia as part of Andy Reid’s staff. Ironically, it was Castillo who replaced McDermott as the Eagles defensive coordinator in 2011.Despite a public endorsement from head coach John Harbaugh last week, Castillo’s influence moving forward appeared uncertain with the hiring of Roman, who specializes in the running game and uses man, gap, and zone concepts. Castillo is known for coaching more zone blocking and had struggled to establish a productive running game in three of his four seasons in charge of the Baltimore offensive line.The Ravens finished 26th or worse in rushing yards in 2013, 2015, and 2016 and only saw dramatic improvement in the ground game when Gary Kubiak served as the offensive coordinator in 2014.Frazier joined Harbaugh’s staff in 2016 and revamped a secondary that had dealt with chronic communication issues in past seasons. The Ravens finished ninth in the NFL in pass defense, and that included their dramatic struggles without top cornerback Jimmy Smith over the final four games of the season.It remains unclear how the Ravens will proceed as they must now fill their quarterbacks coach, offensive line coach, and secondary coach positions. It was announced on Thursday that former tight ends coach Richard Angulo would become the assistant offensive line coach, but Harbaugh will likely need to make an outside hire to fill Castillo’s job.Defensive backs coach Chris Hewitt was previously in charge of the secondary before Frazier was hired after the 2015 season, making it possible that he could assume more responsibility for 2017.