What is Chip Kelly doing?

That's the biggest question of the NFL offseason after the Philadelphia Eagles coach — two months after getting full personnel control — turned the team upside down with an unpredictable series of roster moves.

It's not just fans who are confused by what Kelly is doing, it's other people who work in the NFL.

He traded Nick Foles and LeSean McCoy, cut Todd Herremans, Trent Cole, and Cary Williams, and let Jeremy Maclin leave in free agency. He traded for Sam Bradford and Kiko Alonso, and signed DeMarco Murray, Byron Maxwell, Walter Thurmond.

All of this has fans and commentators alike looking for a through line — a single, overarching principle that will make all these moves make sense.

The problem is there isn't one. No one has any idea what Kelly is doing here. Numerous theories have popped up, only to be debunked when Kelly pulls the trigger on another move out of nowhere.

Here are the four most popular theories we've seen so far, and why they are wrong:

Theory #1: Chip Kelly traded LeSean McCoy because he thinks his system is all that matters and he doesn't need expensive players at the skill positions.

Debunked because: He signed DeMarco Murray for $21 million guaranteed.

Before Kelly traded McCoy to Buffalo for linebacker Kiko Alonso, Herremans went on sports radio in Philly and said that Kelly believes in his system so strongly that he thinks he can plug in any player and score points.

When McCoy got traded, the dominant narrative became: Chip Kelly thinks his offense will take care of itself so he doesn't need an expensive running back. He would have good reason to think this way. He turned a four-win team into a 10-win team in his first year in Philly, and made Foles look like one of the best quarterbacks in the league in the process.

Combine trading McCoy with cutting Desean Jackson in 2014 and letting Jeremy Maclin walk in free agency, and it was starting to look like Kelly didn't believe investing heavily at the skill position.

... And then he gave Murray, who carried the ball 392 times last year and has a history of injury, $21 million guaranteed.

Theory #2: Chip Kelly's plan is to buy low on guys with shaky injury histories.

Debunked because: He's also spending a ton of money, which doesn't really jive with "buying low."

This theory popped up on Twitter on Wednesday amid reports that the Eagles were going to sign free agent running back Ryan Mathews. He'll join Alonso, Bradford, and Thurmond on the list of free agents coming off injuries who Kelly signed this offseason.

The Eagles, more than any other professional sports team except perhaps the Phoenix Suns, have a reputation for being all-in on sports science. There are countless articles about Kelly's outside-the-box practice habits, use of secretive and unusual training equipment, and belief in personalized smoothies.

When it seemed like the Eagles were signing all these injured guys, a lot of people sneered: CHIP THINKS HE CAN CURE THEM WITH SMOOTHIES.

The problem with this is he's not exactly "buying low." He spent $21 million on Murray. He gave up a ton to get Bradford. And he gave away the team's best offensive player to get Alonso. It'd be one thing if he was picking up all these guys for nothing. But he's actually investing significant resources in all of them. He's paying full price.

Theory #3: Chip Kelly is going for a full, 76ers-style, rebuild from the ground up.

Debunked because: He's basically spending all the money he can get his hands on.

It's true that Kelly cleaned house. He got rid of starters at quarterback, running back, wide receiver, corner, offensive tackle, and defense end. He might not be done either.

But he also appears to be replacing the guys he got rid of with veterans who will allow the team to win now. He's not maximizing cap space and collecting draft picks to build for the future, he's replacing parts on the fly in order to be competitive in 2015.

You aren't in rebuilding mode if you give Byron Maxwell $25 million, DeMarco Murray $21 million, and Sam Bradford $13 million (and also give up a 2nd-rounder for him). Even before the Murray deal, the Eagles only had $13 million in cap space, the 11th-lowest amount in the league.

Theory #4: Chip Kelly is doing all of this as some master plan that ends with Marcus Mariota in an Eagles uniform.

Debunked because: He gave up assets to get Bradford that could have been used in a Mariota trade.

It would take a massive haul for the Eagles to move up from the 20th pick to draft Mariota. In denying the rumors that he wants to trade up for the Oregon QB, Kelly said he'd never mortgage his team's future for a single player.

Whether that's just posturing or not, if the Eagles wanted to trade up, they would be collecting assets to use in a package right now. Instead, they're getting rid of them.

They swapped a 4th-round pick for a 5th-round pick in the Bradford trade, and also gave up a 2016 2nd-rounder in addition to Foles. That sort of investment not only suggests Kelly sees Bradford as the quarterback of the future in Philly, it makes it harder to trade up to get Mariota.

Here's what Kelly said about Mariota yesterday:

"Let's dispel that right now. I think that stuff's crazy. You guys have been going with that stuff all along. I think Marcus is the best quarterback in the draft. We will never mortgage our future to go all the way up to go get someone like that because we have too many other holes that we're going to take care of."

Maybe we'll have a better idea of Kelly's plan once free agency and the draft are over. At least we'll be able to take in the sum total of all his moves so far. Right now, every time you think you have a handle on what he's doing, he makes a move that throws everything into chaos again.

*This post has been updated to reflect the Ryan Mathews signing.