BLACKSBURG -- Kirk Herbstreit called Virginia Tech's Bud Foster the other night.

In preparation for ESPN's Monday prime-time matchup between Boise State and Virginia Tech, the color analyst started picking the brain of one of the country's most renowned defensive coordinators about how he plans to slow down an offense that led the nation in scoring last year.

"[Herbrstreit] asked some philosophical stuff and all that,'' Foster said Wednesday night. "But, hell, one of my big concerns is -- and you see it in a lot of [early season] college football games -- is not sharp tackling.

"Because you don't get as much full-speed work, you don't have scrimmages like you do in high school where you go against other people, other backs. We're not tackling the quarterbacks, very little ... just in space and you're blowing quick whistles, and you're getting some scrimmage work, but it's limited.

"In the NFL, they got four preseason games. That's the one area in college football where you see big plays and special teams early on. And you see missed tackles, whether it's on defense or on special teams.''

Foster said today's game-week practice menu will include circuit drills, meaning wrap up and tackle somebody.

"It's going to be a point of emphasis in our team time,'' Foster said. "We've been doing so much team good on good and we're two-hand touching, and this week we're wrapping up all the ballcarriers, and on the scout team, we're doing all that. If not, I'm going to bring them back and do it again. We've got to be sharp on that part of it.

"It's about angles, effort, leverages, and the only way you can get that done is do it at full speed. Now we're not tackling to the ground. We're thudding up. We've got to get our head across the bow. We're going to emphasize that not only in the individual part but all in the team parts.''

Foster said the tackling has been "so-so'' in live scrimmages.

''We've had some young guys who collision-hit rather than wrap up,'' said Foster, whose biggest concern heading in the opener is a backup cast littered by inexperience and youth.

"In high school, you can do that, but at this level where the backs are Darren Evans or Ryan Williams or David Wilson, you can't collision tackle those guys because they will stay on their feet. Those are some things that the young kids have had to learn.''

Switching up

Since last Saturday's final preseason scrimmage in which the No. 1 offense torched the No. 2 defense, Foster and his staff have made some changes.

First-team rover Davon Morgan has been getting some No. 2 reps at whip linebacker, where the depth behind new starter Jeron Gouveia-Winslow has been stripped by injuries to Alonzo Tweedy, Lorenzo Williams and Zach Luckett.

Redshirt junior Jacob Sykes, projected as the No. 2 behind Rashad Carmichael at boundary corner, has been getting some backup work at free safety, where No. 2 free safety Antone Exum has been moved to backup rover.

''We're going to play 11,'' Foster wryly said. "We've moved some guys around to get them in position to help the football team. Some of the backup guys will have some growing situations, so we're moving some guys around in some backup spots who were starters, getting them a few reps in case there's an injury or that type of thing.''

Sykes' move has opened the door for Kyle Fuller, who will be one of two freshmen to play Monday. Fuller, the younger brother of ex-Hokies star Vinnie Fuller, is now taking No. 2 reps behind Carmichael at boundary corner.

Redshirt freshman Telvion Clark also is getting some backup reps at the backer spot behind starter Lyndell Gibson.

"I don't think we've got enough quality depth at backer and whip,'' Foster said. "At whip, it has been injuries. At backer, it's just young and inexperienced and they haven't been consistent in their performance."

Quick kicks

Redshirt freshman defensive end James Gayle, who has missed much of the preseason because of injury, practiced Wednesday. "James doesn't have his timing; there is a lot of things he's got to catch up on,'' Foster said. ... Redshirt freshman J.R. Collins, who has had a strong camp, will be the third defensive end behind starters Steven Friday and Chris Drager.