There is very little Chip Kelly likes less than the notion that his offense can be categorized and placed on a shelf - even a very special, unique shelf - as if it were just another can of peas in the great supermarket of the NFL.

When Cardinals coach Bruce Arians sniffed last week and said Kelly's read-option system was a nice college offense, Kelly didn't seem to mind, or even notice, the criticism. He was more interested in pointing out that the Eagles run a zone-option play now and then, not read-option, and that those plays are just one facet of an offense with many sparkling variations.

As it has turned out this season, he's not kidding about that. Kelly is less tied to the dogma that supposedly trailed him from Oregon than to the goal of beating the other guy with whatever stick happens to best fit his hand that day. He has fiddled and fussed with different combinations and different ways to use his players, and during the current four-game winning streak, he has become increasingly enamored with putting two tight ends on the field at the same time.

This isn't classic Kelly. (It's classic Mike Holmgren West Coast offense, if you want to know the truth.) But for the last month, it has been the best way to create mismatches and win football games. Going with what works is classic Kelly, a coach whose favorite "ism" is pragmatism.

"We feel like we have three [tight ends] that are talented, and when the matchups present themselves, we can exploit it," Kelly said Sunday after Brent Celek and Zach Ertz combined for nine catches and three touchdowns in the win over Arizona.

In the first eight games of the season, the Eagles used multiple-tight-end sets just 16 percent of the time on offense. During the last four wins, that has risen to 42 percent, with most of the difference coming as rookie Ertz has taken more snaps and slot receiver Jason Avant has taken fewer. Celek, Ertz, and James Casey, who has averaged about 10 snaps in the last four games, have combined for 22 receptions in those four wins.

"I think it puts the defense in a bind, whether they want to play their base defense or nickel, because with two tight ends, we can throw the ball or run the ball. They have to make a decision," Celek said.

Kelly is fine either way. If the opponent leaves its linebackers on the field, he thinks his tight ends can beat that coverage. If the opposing defense goes smaller to get better coverage, he's got an answer for that, too. While Celek is the steady prototype of a versatile tight end, Ertz is becoming the wild card because he is an exceptional receiver for his size (6-foot-5, 250 pounds) and is improving as a blocker as well. Teams aren't sure what to do with him.

"You have Brent Celek, who can block and catch touchdown passes, and you don't see many guys who can do that . . . and Ertz can get in there and block good enough and is a huge threat in the pass game," Eagles linebacker Connor Barwin said. "If you put those two guys in together and you're playing against them, I don't know what you do. Do you treat them like an 11-personnel [one running back, one tight end] because of Ertz, or do you treat them like a normal 12 [one running back, two tight ends]? Pick what you want to do and I'm sure whatever they pick, Chip calls something to beat that."

The Detroit Lions, who face that decision on Sunday, have used a nickel formation with an extra defensive back two-thirds of the time, taking linebacker Ashlee Palmer off the field in almost anything that represents a passing situation. But what will the Eagles' two tight ends represent for the Lions?

"A lot of times when we go two tight ends, I'm in the slot," Ertz said. "I feel I have the ability to win one-on-one matchups against either a linebacker or a nickel back. If we call a running play, I'm able to block the smaller guys, or I can run a route against the bigger guy. So I think it's a matchup nightmare."

At least so far, but if teams find a way to better defend against it, Kelly will move on to something else. The Lions are excellent against the run and not-so-excellent against the pass, so the assumption is they will continue their enthusiasm for the nickel to get better coverage and challenge the Eagles to run the ball. By the second half, Kelly may have to move his offense to another shelf entirely.

"It's a week-to-week thing," Casey said. "It all depends on what kind of matchups you think you're going to have. As the season goes on, the offense evolves into what's working best and what gives the defenses the biggest problems. We've been starting to have success with two tight ends, so Coach Kelly and Coach [Pat] Shurmur have been going to it a little more often."

That will keep happening as long as it works, or until the Eagles run into an opponent that presents a better opportunity for a mismatch somewhere else on the field. Maybe it's just a nice, little college offense, but it does have the ability to change majors if necessary. Just ask the professor. He'll tell you.

@bobfordsports