INDIANAPOLIS -- It was an obvious area that Chris Ballard needed to address when he was named general manager of the Indianapolis Colts last January: defense.

Ballard cut ties or didn't re-sign some big defensive names many fans had grown accustomed to seeing on game days. It wasn't personal -- it was just moves that had to be made on a defense that had continued to be poor year after year.

D'Qwell Jackson, Art Jones, Erik Walden, Mike Adams and Trent Cole were all gone by April.

Then Ballard, who is hell bent on making sure he gets the roster he envisions, continued that quest when he released their longest-tenured cornerback, Vontae Davis, on Thursday.

The defense has changed so much that there were instances in which the Colts couldn't see a current player on the screen as they reviewed film of last season's game against the Pittsburgh Steelers.

"There were many times when you could freeze the frame and not one player that was on the field is playing any meaningful downs for us right now," defensive coordinator Ted Monachino said. "So yeah, it's been interesting for sure."

All eyes will be on the Colts' secondary on Sunday against the Steelers.

Rashaan Melvin, Pierre Desir and Nate Hairston are about to learn what it feels like to face arguably the NFL's best trio of receivers in Antonio Brown (835 yards), JuJu Smith-Schuster (424 yards) and Martavis Bryant (234 yards). Melvin and Desir have combined to play a total of two games against the Steelers in their career. The young secondary won't know what to expect when it faces a Steelers passing attack that is ranked ninth in passing yards per game and led by quarterback Ben Roethlisberger.

"That's a good thing sometimes," Monachino said about their lack of experience at cornerback in playing the Steelers. "... They want to go out and test themselves against arguably the best guys in the league, so I'm not at all concerned about those young guys. They'll go out, and they'll compete."

Sunday will be the start of a trial period for the Colts' cornerbacks, a group that also features rookie Quincy Wilson. It'll also be their toughest challenge for the remainder of the season. No other team on the schedule is currently ranked in the top 10 in passing in the NFL.

"Good quarterback, good receivers, good running back," Melvin said. "They do a lot of good things on offense, and as a defender, we always look forward to the challenges. It's another opportunity to go out there and test how good we are and compete and see if we can get a win."

The Colts' secondary is coming off a confidence game in which it helped hold the Houston Texans to only 194 yards passing. But Tom Savage was at quarterback. There's no comparison between Roethlisberger and Savage.

Adding to the already long list of problems this young secondary faces is the fact that the Colts' defense hasn't been able to get to Roethlisberger in recent games. They have not sacked Roethlisberger once in their past three matchups and have allowed the Steelers quarterback to complete 72.2 percent of his passes and average 369 yards passing per game.

The Colts haven't improved much in the sack department, as they're tied for 18th in the league in that category with 18 on the season. It doesn't matter how good your secondary is if you can't put pressure on the quarterback. You can expect your defensive backs to stay plastered to their receivers only for so long before they're able to get open.

"Everybody understands what's coming to town," Colts coach Chuck Pagano said. "You don't need to beat a dead horse. ... You can't give up big plays to [Brown]. Can't allow him to wreck the game, and he's done it over and over and over again. A [future] Hall of Fame quarterback [like Roethlisberger] that has thrown for a ton of yards and completed a bunch of passes and touchdown passes and no interceptions; we know all that stuff. It's why we're excited about the opportunity. It's a chance to do something that nobody will give us a shot at doing."