PITTSBURGH -- With cornerback and wide receiver their apparent biggest needs, the Pittsburgh Steelers went elsewhere in the first round of the draft and for good reason, according to general manager Kevin Colbert.

With the 15th pick of the draft, they took the fastest linebacker available, Ryan Shazier of Ohio State, with the idea he will boost a defense desperate for speed and big plays.

"This guy can flat-out run," said Colbert about the 6-foot-1, 237-pounder who timed at 4.36 seconds in the 40-yard dash at Ohio State's Pro Day. "The offenses continue to spread out and you need speed. You need speed at linebacker, your secondary; you need speed everywhere. This kid has unique ability to make plays not only at him, but plays laterally as well."

The Steelers have come up woefully short doing that the past few seasons. Not long ago one of the most feared defenses in the NFL, the Steelers fell off sharply in 2012 and 2013 in both sacks and forced turnovers. They also slipped from No. 1 in yards allowed in 2012 to No. 13 in the NFL last season.

The Steelers plan to put him at the mack linebacker position next to Lawrence Timmons, their first-round pick in 2007, and it should not take him long to start. Last year's starter was rookie sixth-round pick Vince Williams.

Colbert acknowledged they may have had bigger needs elsewhere, but just could not pass up a playmaker like Shazier, Ohio State's most dominant defender.

"He's a defensive playmaker," Steelers coach Mike Tomlin said. "Bigger than anything, bigger than position needs, what we needed was a defensive playmaker."

The Steelers have just three starters left from their 2012 defense -- Timmons, cornerback Ike Taylor and safety Troy Polamalu. The team weeded out everybody else over the course of the past two seasons in an effort to get younger and faster.

The departed include nose tackle Casey Hampton, defensive ends Brett Keisel and Aaron Smith, safety Ryan Clark, and linebackers James Farrior, Larry Foote and LaMarr Woodley.

Old and slow is how Warren Sapp called that aging defense three years ago. Shazier is now the second straight linebacker taken by the Steelers in the first round. Jarvis Jones, selected with the 17th pick in 2013, saw time at right outside linebacker as a rookie.

Shazier, Jones, Timmons and Jason Worilds give the Steelers a starting quartet of linebackes with speed and explosiveness as they try to rediscover the Blitzburgh formula.

"He is a guy who will be on his feet making sideline-to-sideline tackles associated with today's football," Tomlin said of Shazier. "Quite frankly, the man doesn't have any holes."

Yet after passing up cornerback, wide receiver and defensive line Thursday night, the Steelers still have many.