FLORHAM PARK, N.J.

Bill Parcells had this timeless quote to describe NFL rookies who struggled the way Sam Darnold did during a three-game stretch midway through the season:

“He’s like a ball in tall grass — lost.”

After a mostly promising first six games in which the No. 3 overall pick seemed to pick up more self-assurance as the season progressed, he hit a wall in the next three games. In consecutive losses to the Vikings, Bears and Dolphins, he completed only 47.3 percent of his passes, threw for two touchdowns, was intercepted seven times and had a miserable 43.3 rating.

By the time he lost to the Dolphins, 13-6, his confidence appeared shot. It looked as if he needed a break, even if he would never have thought about asking for one.

A foot injury he suffered in the second half against Miami indeed knocked him out of the next three games, an unanticipated month-long leave that created plenty of uncertainty about what would come next.

As it turned out, the break was the best thing that could have happened to the 21-year-old rookie. In the three games since his return, Darnold has looked like a completely different player. He has completed 66 percent of his passes, thrown for six touchdowns, been intercepted only once and produced a 106.2 rating. It’s no coincidence.

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Through a combination of watching 39-year-old backup and mentor Josh McCown prepare for games and working on his technique — particularly his footwork and his recognition of pass defenses — Darnold has taken a giant leap forward in his progression as a quarterback.

“I think just settling my feet down, that was a big thing,” he said. “Just calming my feet down and understanding where my checkdowns are, understanding what coverages that I can get the ball down to the back, what coverages I can expose the defense and possibly hit a receiver down the field. I think that’s really how I’ve grown the most, and I’m just going to continue to try to do that and continue to grow with that.”

It has been a welcome development for Darnold and for a franchise hoping that he can be the answer to what the Jets have needed for years. For decades, in fact: a championship-caliber quarterback.

There still is a long, long way to go for Darnold, but he has done all that realistically can be asked of a first-year quarterback. His recent improvement speaks to his talent, resilience and growth potential.

Give McCown, as well as offensive coordinator Jeremy Bates and quarterbacks coach Mick Lombardi, a heaping amount of credit for Darnold’s development. It was especially important to McCown that Darnold learn while he sat out, and he did everything possible to show his rookie counterpart how to get through his early struggles.

Perhaps the greatest wisdom McCown imparted was how to better deal with complicated zone defenses opponents used against the Jets.

“It’s about playing fast, especially when you’re dealing with zone coverages,” he said. “Processing quickly, getting the ball out of your hands, taking completions. That’s kind of natural for my game. That’s how I have to play, because I don’t have a big arm like he does. I know for me as a young guy, it was very helpful to watch [another guy] do it.”

Once Darnold returned, it all made sense. As his mind sped up, the game slowed down for him and his decision-making became much clearer.

“He had played enough games [before the foot injury] to match what he was seeing back there with what he was seeing from the sideline,” McCown said. “It’s like, OK, this is what it looks like from the side and this is what it looks like when you’re in there. That guy really is open, or the [defensive backs] are really getting deep, so let’s just check the ball down and get rid of the ball. That’s what I’ve been most impressed with is just how fast he’s playing.”

It has been important that McCown do everything possible to assist Darnold. He pointed to Sunday’s opponent — the Patriots — as an example of how critical it is to establish quarterback consistency.

“Look no further than this weekend what stability at that position means to a franchise,” said McCown, referring to Tom Brady’s wondrous career. “If we can get that, that’s huge for this organization and for Jets fans for years to come. I see that and that’s what gets me excited, because I want that for everybody.”

No longer a ball in tall grass, Darnold has found his way forward. He’s not lost anymore.