Renowned for their defense for what seems like decades, the Pittsburgh Steelers were much better on offense last season, and it appears a sea change has occurred. The Steelers -- led by a future Hall of Famer at quarterback and loaded with veteran superstars -- could be second to none in the NFL on offense in 2015. Meanwhile, a youth movement on defense will be in full swing.

All signs indicate the Steelers will need to rack up points in hopes of winning a playoff game for the first time since the 2010 season, and that's not how they're used to operating. It's as if the Steelers suddenly are in the Bizarro World, the comic book planet where everything is the opposite of what you'd expect. From the look of things, they could be there for a while.

"When you think of the Steelers, you think of defense first, and that's always the way it has been," former Steelers safety Ryan Clark, an ESPN analyst, said on the phone this week.

"So is this strange? Yeah. It's really strange."

No one understands that better than Clark. For eight of his 13 NFL seasons, Clark, who retired after playing for the Washington Redskins last fall, was a Steelers team leader. During that time, Pittsburgh won two AFC titles and one of its record six Lombardi trophies. "There's a culture on defense," Clark said. "There's a level of expectation that few teams have ever had."

No doubt.

When fans still revere a defensive line from the 1970s -- the "Steel Curtain" provided the foundation for four Super Bowl victories in six seasons -- there's no question about your franchise's identity.

Beginning with the 2005 season, which the Steelers capped with a Super Bowl win, they finished in the top 10 in total defense for eight straight seasons, including leading the league four times. On offense in that period, Pittsburgh ranked high among the league leaders only twice, finishing no better than seventh in total yards. There was nothing unusual there.

Then last season, it all flipped: Pittsburgh finished second in total yards.

Ben Roethlisberger topped the NFL and broke his team record with 4,952 yards passing. Roethlisberger's 32 touchdown passes matched his franchise mark. In running back Le'Veon Bell's second season, he emerged as the every-down monster the Steelers hoped he would become, leading the league in yards from scrimmage. (Bell faces a three-game suspension to start the season for violating the league's substance abuse policy.) Wideout Antonio Brown was a big-play artist. The offensive line took a step forward, and if there's a better center than Maurkice Pouncey, no one seems to know it. That group formed the core of the Steelers' strength.

Meanwhile, the defense struggled.

Keith Butler will be taking over what has been Dick LeBeau's defense for years. George Gojkovich/Getty Images

The Steelers plummeted from first overall in 2012 to 13th in the 2013. Of course, from the Steelers' perspective, the drop-off could have been an anomaly. It wasn't: The Steelers tumbled to 18th last season. They hadn't been so low since ranking 22nd in 1991. And they're about to get younger.

Considering that Pittsburgh went 11-5 and reached the postseason, it was clear that the offense had to do too much heavy lifting. Changes were inevitable.

Legendary coordinator Dick LeBeau, the architect of Pittsburgh's innovative 3-4 zone blitz, moved on to run the Tennessee Titans' defense. Iconic safety Troy Polamalu and standout cornerback Ike Taylor retired, continuing a trend of the Steelers losing cornerstone players. It's an old story, Clark said.

"They tried to keep a core of guys together who were good defensively for a long time, and they were so good, but they kind of all aged out together," he said. "Some of the young guys they brought in ... they're kind of still waiting for those guys to become good players."

It's now Keith Butler's job to help them develop. Butler, Pittsburgh's former linebackers coach, waited a long time to run his own shop. In a sense, Butler takes over at the perfect time, with youth on the roster and management eager for a fresh approach.

That doesn't mean Butler will scrap the 3-4. Considering how much success Pittsburgh has had, a complete change in philosophy would be downright silly. And risky, too. Like any coordinator, though, Butler plans to put his stamp on the group. Getting more from those underachieving high-round picks would be a good place to start.

The Steelers have selected defensive players during the first round in four of the past five drafts, including linebackers three consecutive years. But linebackers Jarvis Jones and Ryan Shazier, the Steelers' top picks in the 2013 and 2014 drafts, respectively, must first prove they can stay on the field.

Although no one on the Steelers is capable of replicating what Polamalu accomplished during his prime, is inexperienced safety Shamarko Thomas even ready to try? The Steelers are counting on No. 1 pick Bud Dupree to deliver as an edge rusher. And after losing his starting spot, will cornerback Cortez Allen get it together and help fill a void left by Taylor's departure?

The good news? The offense, obviously, Clark said.

"You look at their offense and you know they'll win games," Clark said. "You look at the combination of having Big Ben, Bell, Brown and an offensive line that has come together -- they'll score points and they'll be in a lot of football games. But I don't know if the culture of Pittsburgh is really built to love that kind of football."

It'll be interesting to see. But after the Steelers did it one way for so long in their world, perhaps their fans are ready for the Bizarro Steelers.