New York Jets quarterback Justin Fields during a joint practice...

New York Jets quarterback Justin Fields during a joint practice with the New York Giants at training camp in Florham Park, N.J., on.Tuesday. Credit: Ed Murray

FLORHAM PARK, N.J. — Aaron Glenn spent most of Tuesday’s joint practice with the Giants watching how the Jets’ offense operated. He left the field knowing the first team has to perform better overall.

Justin Fields started fast but then he and the rest of the starting unit hit a lull. The Jets’ offensive line had difficulty keeping the Giants’ front from pressuring and getting to Fields. He was unofficially sacked four times.

“I thought it was up and down,” Glenn said of the offensive line’s performance. “I thought there were some times we protected real well, but there were some times we got beat too.”

Brian Burns was disruptive and in the Jets’ backfield a number of times. Rookie Abdul Carter moved around up front and moved players, blowing through Joe Tippmann one time. Dexter Lawrence batted down a pass.

“It's good for our offense to be able to see that,” Glenn said. “You don't go against a front like that on an everyday basis and every week basis for the most part.”

Up and down was also the phrase Glenn used to describe Fields’ play as well.

Fields completed his first five passes in team competition. One was a strong throw to Tyler Johnson on the sideline after Fields was flushed out of the pocket.

He finished the day 7-for-11 with a touchdown. Fields’ last pass was a nice sidearm throw to Jeremy Ruckert in the end zone for a touchdown during a red-zone period.

“The first two periods I thought we did well,” Fields said. “That third period could have been better. Other than that, I think we did all right. I’m always going to say that there’s room for improvement.”

Glenn thought Fields displayed his mobility against the Giants’ pass rush but he would have liked to see Fields get rid of the ball quicker.

“One thing we got to do is when we see the guy let’s get it out,” Glenn said.

Fields had a strong showing in Saturday’s preseason win over the Packers. He led a touchdown drive using his arm and legs in his only series. Fields and the Jets are looking for more consistency.

Glenn wanted to reserve full judgment until he again watched the film of Tuesday’s practice. He thinks the offense will be better after seeing it.

The Jets will travel to the Giants’ facility on Wednesday for another joint practice in advance of their preseason game Saturday at MetLife Stadium.

“They’re a talented front,” Glenn said. “For all those guys to get a chance to go against somebody new with different skill sets is always good. To get a chance to go back and look at the tape and then do it again the next day, I think our guys will end up watching it and being better the next day, too.”

Tyrod Taylor gets scoped

Backup quarterback Tyrod Taylor had a “minor scope” on his knee, Glenn said. The Jets hope Taylor will be back for Week 1. If not, Adrian Martinez or Brady Cook could be Fields’ backup.

Martinez played better than Cook in the preseason game and Monday’s practice. Cook, who has had some good days in camp, hurt his ankle after being stepped on late in practice. Glenn didn’t think it was serious.

Jermaine Johnson returns

Edge rusher Jermaine Johnson, who was activated from the PUP list Monday, stretched and warmed up with the Jets but then worked on a side field. Johnson is returning from a torn Achilles tendon. He hopes to start getting in team drills Wednesday, but the Jets will take it slow.

“I feel ready to go,” Johnson said. “But I trust them. I like to say, they’re backing a Ferrari off the truck a little cautiously right now. I understand it, but I feel ready to go.”

Johnson added, “When they take the leash off me it’s going to be fun.”

Injury updates

Mason Taylor, who missed last week with a high ankle sprain, returned to practice and made a nice diving catch during team periods . . . Quinnen Williams (calf) was back on the field, but he worked out on the side . . . John Simpson (back) practiced for the first time in nearly two weeks . . . Allen Lazard will be out for two weeks after hurting his shoulder on Saturday. His status for Week 1 is unclear.

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