Mathis cut again shows Kelly's belief in system

The latest discarding by Chip Kelly has resurrected the familiar trope about the Eagles coach - that he whacks those who dare to cross him, all in the name of "culture over scheme." But what that line of thinking often overlooks is Kelly's stringent belief in his offense.

It was likely a confluence of factors that led to the release of Evan Mathis on Thursday. But Kelly would have never parted with the two-time Pro Bowl guard unless he was convinced the offense could function at a high level with what on paper looks like a weaker offensive line.

Allen Barbre replaces Mathis at left guard, and Matt Tobin, Andrew Gardner, and Dennis Kelly will slug it out for the right guard spot that Barbre was initially penciled in to fill after Todd Herremans was released in February.

Kelly still has time to search for another guard from what's left in free agency (journeyman Jared Wheeler will work out for the team on Monday) or manufacture a trade. But it's unlikely he'll find one anywhere near Mathis at his norm. If anything, Kelly has spent the last two offseasons replacing most of the parts on offense with younger and cheaper alternatives, and he already has that on the roster.

Kelly said in March that he was leveling an Eagles salary cap that was heavily tilted toward offense. But almost all of his controversial moves have come on the offensive side of the ball, and he hasn't necessarily replaced the departed with upgrades, or at least with players who don't have question marks.

Wide receiver DeSean Jackson was released last year and was essentially replaced by Jeremy Maclin, who was coming off a torn anterior cruciate ligament. The argument was never one or the other. Kelly could have had both. But it's fair to say that gamble paid off even if the offense wasn't as good as it was in 2013.

This offseason - Kelly's first in full control of personnel - running back LeSean McCoy and quarterback Nick Foles were traded, Maclin left via free agency, and now Mathis is gone with just days to go until the Eagles break before training camp.

DeMarco Murray may be seven months older than McCoy, but his 2015 salary cap number is $6 million less than what McCoy's would have been. But aside from last year, when he played all 16 games and led the NFL in rushing, Murray never went a full season without injury. McCoy had only missed time because of one injury and played all 16 games in each of the last two seasons.

The resounding theme from the Eagles, however, has been that Murray's one-cut running style is better suited to Kelly's scheme, in which the yards are presumably there for the taking.

Quarterback Sam Bradford, acquired in the Foles trade, has more upside in Kelly's quick-trigger offense than his predecessor, but only his left knee knows whether he'll be ready for the opener or can survive an entire season.

Jordan Matthews and Nelson Agholor could offset what the Eagles lost in Jackson and Maclin - and don't forget underutilized tight end Zach Ertz when calculating where pass-catching production could come from - but that may be expecting too much too soon from young receivers.

Jackson and Maclin had career years in Kelly's offense, though, as did McCoy. Don't think Kelly hasn't noticed.

Which brings us back to the offensive line, where gauging production can be difficult. Kelly's offense isn't some magical potion for rushing yards, but even with last year's injuries up front, the Eagles ranked ninth a year after leading the league.

Kelly has invested in the run game, extending tackle Jason Peters and center Jason Kelce and adding Murray, Ryan Mathews, and Darren Sproles the last two offseasons. But he hasn't drafted a lineman since tackle Lane Johnson in 2013 and will rely on some combination of Barbre-Tobin-Gardner-Kelly (weren't they supposed to address depth issues?) at both guard spots.

Mathis excelled in run-blocking. He was one of the best guards in that discipline even before Kelly arrived. Both Andy Reid and Kelly's offenses relied heavily on zone-blocking, where quickness is more important than power, but Mathis had perfected the art.

Barbre is athletic, but he has played in only two games for the Eagles over two seasons. Tobin moves well, too, but he was benched in favor of Gardner after Herremans was lost for last season. Both had more problems in pass protection, particularly on third down, when the benefits of Kelly's offense and the threat of running aren't as great.

Bradford's quicker release should help in the yin and yang relationship between a quarterback and his line, but shouldn't protecting the oft-injured Bradford be paramount? Didn't Herremans say this offseason that Kelly wants to build from the quarterback-line out?

Which made it all the more surprising that he parted with Mathis without receiving anything in compensation. He did the same with Jackson, who did more to grease his departure than Mathis, who never publicly asked for a new contract and missed voluntary workouts only this spring.

Kelly believes in culture-building. There is a hint of hubris in his decision-making. And you had better not step out of line with his rigid view of what constitutes an NFL player.

But Kelly's unwavering faith in his system drives the engine.

@Jeff_McLane