Key No. 4: Defensive line needs to rise for Steelers

This is the fourth in a series as we look at the five positions that will hold the key to the 2015 season that begins Sept. 10 in New England. We will provide a general rundown, identify the strength and weakness and pick the one player who is ready to have a breakout season.

Today: No. 4, Defensive line

RUNDOWN

For the first time since 2004, the Steelers will have someone other than Dick LeBeau running their defense.

Keith Butler, who worked under LeBeau for all 11 years, is the new defensive coordinator and will implement changes in how the team rushes the quarterback and defends the pass.

And the Steelers think they have the ingredients to have a pretty good three-man line with defensive ends Cam Heyward and Stephon Tuitt and nose tackle Steve McLendon. Problem is, there isn’t much behind them.

But what is behind them is massive.

That would be tackle Dan McCullers (6-8, 358), whose size makes him almost unstoppable collapsing the pocket. The Steelers think they can take advantage of that in their sub-packages to generate more pressure up the middle.

Heyward, though, is the star. At 25, he has emerged not only as a leader of the defense, but also one of the best ends in the league. He tied for the team lead with 7 1⁄2 sacks and led the team with 21 quarterback hurries in 2014, healthy totals for a 3-4 defensive end.

Tuitt, a No. 2 pick last season, came on late in his rookie season and showed great development. With Heyward, that gives the Steelers hope for the future that the young duo can form a bookend tandem similar to Aaron Smith and Brett Keisel.

While the run defense improved six spots to No. 6 in the league, allowing an average of 100.3 yards per game, the Steelers still allowed 11 runs of 20 yards or longer (10th most in the league) and their per-carry average of 4.4 yards was seventh worst in the league.

Those numbers were worse than 2013 when they ranked 12th in the league and allowed seven runs of 20-plus yards and an average of 4.3 yards per attempt.

Rookie L.T. Walton has a spot waiting for him on the roster., but the Steelers would like to see him earn that spot. Veteran Cam Thomas could still be a training-camp casualty.

STRENGTHS: Heyward has developed into one of the best 3-4 defensive ends in the league and is equally adept pressuring the quarterback and stopping the run.

WEAKNESSES: Lack of depth prohibits will restrict any type of quality rotation, though McCullers should be a good sub-package substitute.

BREAKOUT CANDIDATE: Tuitt. He came on late in the 2014 season when he had a chance to start five games, including the postseason, and develop. He could become even more disruptive if No. 1 pick Bud Dupree becomes a player on that side in his first year.

NEXT: Offensive line