Fletcher Cox, Mychal Kendricks, Vinny Curry and Brandon Boykin have been through a lot in their short tenure with the Eagles. They were all rookies on defense last season, playing with varying degrees of success. That ranged from Kendricks, a second-round pick who started all but one game at outside linebacker, but wore down as the season went along; to Cox, the first-round pick at defensive tackle who slowly developed into a reliable starter; to Curry, another second-rounder at defensive end who struggled to get on the field and then make an impact when he did; to Boykin, a fourth-rounder who had an up-and-down season as a slot cornerback. In theory, it’s supposed to get easier now that they have a full season under their belts. The reality is that all four players are playing for their third coach and their third defensive system in three seasons going back to their final season in college. The defensive system of head coach Chip Kelly and coordinator Bill Davis is much different than what they experienced under previous coach Andy Reid. “It’s all about being professional about it,” Cox said. “And being coachable and dealing with the situation as best you can, knowing it’s a business.” Cox, for one, is playing both defensive tackle and defensive end under Davis’ hybrid 3-4 front, as opposed to strictly playing defensive tackle last season. Curry is playing defensive end and also getting chances at outside linebacker. Kendricks is moving to inside linebacker, while Boykin is getting chances both at slot corner and on the outside. “I did the same thing in college, moving around a whole lot,” Cox said. “Defensive end, defensive tackle — it didn’t matter where I was. In certain packages, certain situations, they want me outside or they want me inside. That’s the most fun part about it. I get to see a lot of different looks, not just the same look inside.” Cox didn’t crack the starting lineup last season until the seventh game. But he still tied for the team lead last season in sacks with 5.5, and ranked fifth among all rookies and fifth among all defensive tackles in sacks.