New quarterbacks, rising backups and a new defensive scheme led by a new/old defensive coordinator are on the menu for Georgia Tech’s spring scrimmage.

“I hope (fans) can see guys flying around, having fun playing football,” linebackers coach Andy McCollum said. “It’s an honor to play at Georgia Tech. Every time you step out there, you’ve got to play like it.”

The scrimmage will conclude Tech’s spring practice, which has been marked by the absence of several starters because of offseason surgeries, the hire of quarterbacks and B-backs coach Bryan Cook to replace Brian Bohannon and the installation of defensive coordinator Ted Roof’s 4-3 defense.

Five things to watch for from the game, which starts at 7:30 p.m. at Bobby Dodd Stadium, weather permitting:

New under center: Both Justin Thomas and presumptive No. 1 Vad Lee can show fans the future of Tech quarterbacking. Lee will quarterback the first team and Thomas the second team.

“If we had a game tomorrow, I feel like I’d be ready to play it,” Thomas said Wednesday.

Both lack the experience of Tevin Washington, the starter for the past 2 1/2 seasons, but have more speed and the potential to develop into superior passers. In three scrimmages thus far, they have shown playmaking ability both on the ground and in the passing game, but coach Paul Johnson also wants to see them avoid mistakes and keep the ball safe.

They also likely will get some work with a new wrinkle, a “diamond” formation in which the quarterback lines up in a shotgun with the B-back behind him and the A-backs closely flanked on either side.

In high school, “I was probably under center not even 10 percent of the time,” Thomas said. “It’s something I’m kind of used to.”

Running to the ball: Among new defensive coordinator Ted Roof's biggest priorities for the spring was better tackling. Players taking the wrong angle to track down ball carriers or failing to bring them down to the ground were shortcomings last season and led to Al Groh's firing.

The defense looked better in Saturday’s scrimmage and made plays behind the line of scrimmage. On Friday night, one element that bears watching is how often backs and receivers are able to break free for long gains either by breaking tackles or outrunning defenders. Big offensive plays can be attributed to excellent blocking, but also to the defense taking the wrong angles or not finishing tackles.

“Because if you take good angles, and you play your pads square, and you play with great effort, then you don’t miss a lot of tackles,” McCollum said. “That’s what we’ve got to do.”

A-back derby: Tech's most competitive position battle probably is at A-back, where, after returning starter Robert Godhigh, there are five and possibly six players competing for the other spot to replace the graduating Orwin Smith. Dennis Andrews, B.J. Bostic, Synjyn Days, Deon Hill and Tony Zenon are in the mix, although Zenon has been out this spring recovering from surgery. Former B-back Charles Perkins moved into that group Monday.

“When I see one of those guys make a play, it encourages me to make a play just to give (A-backs coach Lamar Owens) a bright spot just to keep your name up there,” Bostic said.

Andrews, a rising redshirt freshman, was the star of Saturday’s scrimmage. It might be someone else’s turn Friday.

Understudies' opportunity: With no fewer than seven projected starters out for Friday, either having missed all of spring practice or suffered an injury in the midst of it, plenty of backups have had a chance to get more practice time and show coaches what they can do.

Friday will be the last chance this spring to make an impression. B-back Broderick Snoddy, safeties Lynn Griffin and Chris Milton, guard Trey Braun and offensive tackle Chase Roberts are among those who have caught coaches’ attention over 14 practices.

Outside linebacker Quayshawn Nealy, who starred in the 2011 spring game on his way to a starting job that season, picked out nose tackle Jimmie Kitchens as the most improved player on the defense.

In the past, the typical pattern for Kitchens, a rising sophomore, was that he “will do something good and then follow it up with something that he does bad, but lately, Jimmie Kitchens has been doing the right thing, making big plays,” Nealy said. “He really has turned around.”

Check the skies: With thundershowers in the forecast for Friday, the concert and other pregame festivities have been canceled, as well as the postgame fireworks display.

The game will be played if at all possible, as a postponement to Saturday is not an option because of scheduling commitments for coaches, team members and game personnel. Fans can check ramblinwreck.com Friday for updates. Tech’s baseball game against N.C. State at 3:30 p.m. Friday is still scheduled, though also subject to the weather.