Every Jaguars assistant coach stands behind the line of scrimmage during practice, putting them close enough to the action to bark pre-snap instructions and be in the huddle moments later. Except for DeWayne Walker. Walker, the team’s new defensive backs coach, stands 30 yards away from the football, between the hash marks. It is from that view Walker oversees part of what could become the youngest secondary in the NFL this year. Out: Safety Dawan Landry (30) and cornerbacks Derek Cox (26), Rashean Mathis (32), Aaron Ross (30) and Will Middleton (26). In: Cornerbacks Alan Ball (28), Dwayne Gratz (23), Jeremy Harris (22) and Demetrius McCray (21) and safeties Johnathan Cyprien (23) and Josh Evans (21). Walker said “no question, no doubt about it,” it will be the greenest defensive back group he’s coached. The Jaguars hope the newbies, when combined with safety Dwight Lowery and cornerback Mike Harris, become a unit that is younger, faster, more durable and better able to play the in-your-face, physical style of coverage being installed by coach Gus Bradley. After signing only Ball in free agency, the Jaguars went to work during last week’s draft, using five of their eight picks on defensive backs. “That’s a first for me,” Walker said. “But all of these guys were needed and they all bring something to the table.” They’ll be needed to help a defense that had only 12 interceptions last year, lacked any kind of consistency (injuries and ineffectiveness) and weren’t difficult to prepare for or play against. It’s possible the Jaguars could start two rookies in the secondary on Opening Day against Kansas City: Cyprien and Gratz. It’s also possible the Jaguars could have six cornerbacks on the Week 1 roster: Ball, Gratz, McCray, Mike Harris, Jeremy Harris and a training camp surprise. In charge of their development is Walker, who spent the last four years as head coach of New Mexico State. He’s back in the NFL for the first time in seven years.