The Browns weren't on the practice field Monday but it was a busy, thorough day of film study one day removed from a disappointing, 31-10 loss to the New York Jets.

Here's what stood out from the first postgame Monday of the 2015 season.

1) Diagnosing the run defense issues

From Day 1 of the offseason up until Sunday's season opener, the Browns' top priority on defense was to be better against the run.

That held true for the first half against the Jets, who managed 42 yards on 12 carries through the first 30 minutes. The second half, though, was not what Cleveland wanted, and the Jets came away from the season opener with 154 yards and an average of 4.3 yards per carry.

Pettine attributed the disappointing result to a number of factors. The first thing he listed, missed tackles, was echoed by inside linebacker Christian Kirksey as an area of emphasis during the team's film analysis. The No. 1 culprit, however, was runs to the edge, a problem that persisted throughout the preseason and was only made tougher when Scott Solomon went down with an ankle injury early in the first quarter.

The interior, Pettine said, was "pretty solid," and rookie nose tackle Danny Shelton played "pretty well" in his first official NFL game.

"He did a good job handling double teams. His pads got up a couple times, but I think for the most part he controlled the middle when he was in there," Pettine said. "We need to be better on the edges."

Pettine reaffirmed his confidence that the run defense would be significantly improved from last year, when the unit finished last in the NFL. Sunday's showing put the Browns 30th in the league after Week 1.

"I thought we did a much better job in practice," Pettine said. "We did a much better job at times in the preseason games. It needs to be played better and it needs to be coached better."

2) Run game issues went beyond O-line

Pettine's critique of the Browns' rushing offense immediately after Sunday's game focused heavily on the offensive line.

After watching the film Monday, Pettine said the team's running backs "left some yards out there."

"We need to break more tackles," Pettine said. "We can't be one and done with our backs. It is going to be rare where it is going to be blocked and a gaping hole and you are running untouched for a while. We are going to have to make some guys miss. We are going to have to break some tackles. That needs to be a point of emphasis for us.

"Overall the running game – we knew it was going to be tough against that front given their history and scheme wise with what they play, but we should have run the ball better."

The Browns finished with 104 yards on 28 carries. Only 46 came from running backs Isaiah Crowell (20), Duke Johnson Jr. (22) and Shaun Draughn (4).

"I think we can come back to the drawing board and fix some things up," Johnson said. "It was all little things that we can fix and we just didn't do it in the game. Now we are coming back to the drawing board and we are going to get it right."

3) Dwayne Bowe update

Pettine said veteran wide receiver Dwayne Bowe, who was inactive Sunday, had a minor setback with his hamstring injury during practice last week and was not 100 percent at the end of the week.

Bowe, who played in the Browns' final two preseason games, was listed as "limited" throughout the week and was deemed "questionable" Friday.

"Just given our numbers it would have been hard to justify having up that many receivers given the game plan," Pettine said. "It was the decision we made."

4) Something to build on

Asked to identify a positive from Sunday's loss, wide receiver Brian Hartline pointed to the Browns' third-down conversion rate against the Jets.

Cleveland converted its first four third downs on a game-opening series that drained nearly 10 minutes off the clock. Johnny Manziel's 54-yard touchdown pass to Travis Benjamin came on a third-and-19. On the previous play, Manziel scrambled for 22 yards on a third-and-4 only to have it wiped away by a chop block penalty on Crowell.

The Browns finished 8-of-16 on third downs.

"We were staying on the field for the most part. The ones that we didn't convert a lot of them were self-inflicted wounds from holding or turnovers or anything like that," Hartline said. "I think that was the positive. I think we will continue to build on that, but overall I think there were some times in the red zone where we should have got the ball in the end zone to keep the points going up. We will continue to move forward."

5) Other observations

• Pettine did not have an update on the status of Solomon.

• A quote to note from Pettine's opening statement at Monday's press conference.

"Lot of good teaching moments in the game, but we cannot be repeat offenders," Pettine said. "Mistakes that we made yesterday we have to make sure that we learn from and do not repeat. That is both from a coaching and a playing perspective. That is where we are today. Disappointed, but anxious to get onto this next one and put on a performance in front of our home crowd that they deserve to see."