Column: The things we didn’t know about NFL season could fill Chip Kelly’s playbook

The map of this NFL season is filled with twists and turns. There are surprises around every corner, unexpected resurgences and startling collapses.

It was pretty clear from the start, for instance, that the San Francisco 49ers were headed for a fall, with all the retirements and other departures, including that of coach Jim Harbaugh. But not many people expected the Indianapolis Colts, Baltimore Ravens or San Diego Chargers to stumble the way they have.

Before the season started, Las Vegas oddsmakers made the Green Bay Packers 11-to-2 favorites to win the Super Bowl. Not a shocker. But those same oddsmakers had the New York Jets at 100-1, and the now-undefeated Carolina Panthers and Cincinnati Bengals each at 50-1.

The historical trend pointed to the Seattle Seahawks taking a dip after losing the Super Bowl. Rex Ryan’s history in the early going with the Jets did not point to him running into problems this early with the Buffalo Bills.

As we approach the midway point of the regular season, some of the forehead-slappers so far:

Peyton Manning’s struggles

With a new coach, a new offensive system, an inexperienced offensive line, and his 40th birthday around the corner, it’s understandable that the NFL’s only five-time most valuable player would see a drop-off in production. Manning’s fade-back has been more pronounced than most expected. He has seven touchdowns, 10 interceptions and a passer rating of 72.5. To put that rating in perspective, his three previous full-season ratings in Denver were 101.5 in 2014, 115.1 in 2013 and 105.8 in 2012. The undefeated Broncos are winning with their top-ranked defense. From Manning’s perspective, the operative word there is “winning.” He put the results in perspective this week, saying: “As the great Ebby Calvin Nook LaLoosh said in ‘Bull Durham,’ ‘I sure like winning. It’s, like, better than losing.’”

Chris Johnson steps up

For running backs, 30 is over the hill. Arizona’s Chris Johnson is clearly still on the ascent, though, with three 100-yard-plus rushing performances in the last five games, including a season-high 122 yards in Monday’s victory over Baltimore. His 567 yards put him second in the league to Atlanta’s Devonta Freeman (621). Although Johnson is one of seven NFL backs to rush for 2,000 yards in a season, that happened way back in 2009. The Cardinals still saw something when they signed him this off-season, even though he was coming off a career-low 663 yards with the Jets.

Perfection abounds

Five undefeated teams remain: New England is 7-0; Denver, Green Bay, Cincinnati and Carolina are 6-0. That’s the most through this point in a season since the AFL-NFL merger in 1970. Last season, nobody even got to 4-0. By the end of the weekend, at least one of those teams will have a blemish on its record, as the Broncos play host to the Packers on Sunday night.

Colt jolt

Everybody is trying to figure out what’s wrong with Indianapolis quarterback Andrew Luck, who is 1-4 as a starter for the 3-4 Colts (who still lead the lousy AFC South). He has nine interceptions to go with 11 touchdown passes, a completion percentage of .562 — behind such players as Jameis Winston, Brian Hoyer and Nick Foles — and his team is coming off back-to-back defeats. He seems to be bothered by an injury to his throwing shoulder, but he hasn’t pointed to that as a problem. This week, tight end Coby Fleener, his teammate at Stanford and with the Colts, came to his defense. “I think the whole ‘Andrew’s poor play’ story is overblown,” Fleener told the Associated Press. “I think you get a lot of the highs and lows as a quarterback. But I think a lot of guys, including myself, need to do a better job of making him look good.”

Chip dip

The Philadelphia Eagles remade their offense this season, getting Sam Bradford in a quarterback swap with St. Louis, and adding running backs DeMarco Murray and Ryan Mathews and first-round rookie receiver Nelson Agholor. So far, on the heels of consecutive 10-win seasons, Chip Kelly’s team is sputtering along at 3-4. Kelly’s offense has taken a statistical step backward in each of his three seasons, yardage rankings dropping from second in 2013 (417.2 yards per game) to fifth last season (396.8) to 15th now (353.1).

Beginner’s luck

San Francisco’s Jim Tomsula is off to a bumpy start at 2-5, but the league’s other two first-time head coaches are thriving. Todd Bowles has the Jets at 4-2 and in good position to bounce back after a loss at New England, and Atlanta’s Dan Quinn has the 6-1 Falcons playing harder than most people expected. Then, there’s Miami interim Coach Dan Campbell. After he replaced Joe Philbin, Campbell s saw his team come to life with back-to-back blowout victories. The Dolphins took a step back this week with a 36-7 beatdown by New England, but at least they’re now showing a pulse.

Follow Sam Farmer on Twitter @LATimesfarmer