4. Cameron Heyward, DL
Cameron Heyward is no young buck anymore. In fact, it's possible that the All-Pro defensive lineman could hang up his cleats for good sometime in the next two years. But even if he may have lost a step from the player we saw 2-3 years ago, Heyward is still a pivotal piece of the puzzle in Pittsburgh.
Heyward has been a full-time starter for a solid decade in Pittsburgh -- earning a whopping 148 starts since 2013. The Steelers have been incredibly fortunate that Heyward has only suffered one injury that has landed on IR since entering the league as a first-round pick back in 2011 (a pectoral tear 7 games into the 2016 season).
With Larry Ogunjobi underwhelming last year and unproven players on the defensive line like DeMarvin Leal and Keeanu Benton, the Steelers aren't going to want Heyward to be absent for a single game this year.
Fortunately, Cam has had outstanding health for the vast majority of his career, but that's obviously not guaranteed to last. Pittsburgh's sample of play without Heyward over the past decade is incredibly small, but knowing the double teams that he demands and the work he can do as both a run defender and pass rusher, I do not want to see what this defense looks like if he's not in the lineup. He's one of the single most important players to the Steelers success this year.