FOXBOROUGH, Mass. -- Offensive guard Joel Bitonio termed it “Jekyll and Hyde.”

But neither Cleveland’s longest-tenured player nor quarterback Baker Mayfield nor even coach Kevin Stefanski could explain it.

How the Browns could look like a legitimate AFC contender one weekend.

Then, a total fraud the next.

The roller-coaster ride continued on Sunday. Just one week after destroying the Bengals on the road to make a statement in the AFC North race, the Browns completely flopped in New England, losing 45-7.

Now an uninspiring 5-5, the clock is ticking on the Browns to rediscover a groove -- to finally string together a series of consistent performances to make a postseason push. Else, become one of the NFL’s biggest disappointments.

“I don’t have the exact answer for that. I wish I did,” said Bitonio, when asked to explain Cleveland’s drastic week-to-week inconsistency. “But we do have to figure it out quick. Because in the AFC, 9-8 is not going to get you in the playoffs.”

Last season, Cleveland surged into its first playoff appearance since 2002 after developing into one of the league's most reliable teams. The Browns didn’t win every game the final two-thirds of the season. But they played up to a certain standard each week, even when COVID-19 sidelined their top players, or, in the case of the playoff opener in Pittsburgh, Stefanski himself.

That resiliency propelled Stefanski to NFL coach of the year honors in his first season in Cleveland and the Browns into the second round of the playoffs. It also positioned Cleveland to be a serious contender coming into this season.

That reliability and resiliency, however, has since vanished. With the two biggest culprits being the quarterback and the defense.

By his own admission, Mayfield has been banged up since Week 2, when he tore the labrum in his non-throwing shoulder. Now battling foot and knee injuries, as well, Mayfield could barely make it from the postgame podium back to the Browns' locker room, walking ever so slowly and gingerly.

Last season, when he ranked No. 3 in QBR from Week 7 to 15, Mayfield looked like the franchise quarterback the Browns had longed for, especially after he guided Cleveland to its first playoff victory in 26 years -- a win over the rival Steelers.

Mayfield has had similar sterling moments this season, most notably last weekend when he torched Cincinnati in a 41-16 rout following days of drama surrounding Odell Beckham Jr.'s eventual release. But Mayfield’s rough outings, New England included, are beginning to overshadow all else. In fact, only twice this season has he posted a QBR above 50 (scale 0-to-100), a feat he accomplished a dozen times in 2020.

“We’ve talked about a certain standard that you set for yourself, and you have to live up to it every day,” said Mayfield, who doomed the Browns with an interception on Cleveland’s second drive, igniting the Patriots' rout. “When you're sitting here at 5-5, obviously something's wrong. So got to figure it out and get it fixed.”

The Browns' defense still has much to figure out and fix, as well.

During the offseason, general manager Andrew Berry poured significant resources into upgrading the defense. He signed four new starters in safety John Johnson III, nickelback Troy Hill, defensive end Jadeveon Clowney and linebacker Anthony Walker. Berry drafted two other new starters in first-round cornerback Greg Newsome II and second-round linebacker Jeremiah Owusu-Koramoah, as well.

At times, the talented Browns defense has been smothering. Five times this season, in fact, Cleveland has held the opposition to fewer than 17 points.

But so many other times, the defense has been a sieve. In fact, since giving up 47 to the Los Angeles Chargers on Oct. 10, the Cleveland defense has surrendered at least 37 points three separate times. On Sunday, the Browns couldn’t stop the run, between and outside the tackles. They couldn’t get pressure on quarterback Mac Jones. And, like so often this year, they couldn’t force a turnover that might have changed the game -- just the way Mayfield’s interception did against New England.

“We are way, way too inconsistent as a team right now,” Stefanski said. “I’ve seen some good moments from our offense, from our defense and from special teams. We just have to put it all together. ... I don’t think there’s any magic wand when it comes to that. We just have to identify and then work at it so that we can play to our full potential.”

Playing up to their full potential, the Browns can look like a Super Bowl contender.

Except, actual Super Bowl contenders don't play that way just half the time.