Bob Glauber Newsday columnist Bob Glauber

Bob Glauber has been Newsday's national football columnist since 1992. He was Newsday's football writer covering the Jets

There really are no guarantees for this sort of decision, something John Mara learned long before he took over as president and CEO of a Giants franchise that has been in his family for nearly a century.

Mara was in college when his father, Wellington, thought he’d hit a home run with defensive whiz Bill Arnsparger, who’d just come off a masterful effort in helping the Dolphins to their second straight Super Bowl victory.

Talk about a hot candidate. Arnsparger was it. But reality set in and he turned out to be an abject failure as a head coach, winning only seven of 35 games before being fired midway through the 1976 season.

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“It’s a different job becoming the head coach,” John Mara said yesterday after introducing new Giants head coach Ben McAdoo, who ascended to the top spot after two seasons as the team’s offensive coordinator under Tom Coughlin. “I learned that in 1974 when we hired Bill Arnsparger, who’s the defensive genius of all time, and it didn’t work out for us back then. Guys can be great coordinators, but it doesn’t necessarily mean they’re going to be great head coaches.”

He’s right. Every year, there are offensive or defensive coordinators who look plenty attractive to head coach-needy teams, only to fall flat once they take over. Dave Wannstedt, Norv Turner and Butch Davis all were highly respected members of Jimmy Johnson’s staff with the Cowboys’ dynasty teams in the 1990s, but none came close to winning a championship as a head coach. Joe Philbin was a highly respected member of Mike McCarthy’s Green Bay staff, but he bombed with the Dolphins and was fired early in the 2015 season.

For every Bill Parcells, Bill Belichick, Joe Gibbs or Bill Walsh, all of whom went on to Hall of Fame careers after serving as NFL assistants, there are plenty of Romeo Crennels, Todd Haleys, Jim Tomsulas and Mike Pettines to tip the scales to the side of failed head coaches.

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But Mara’s intuition tells him McAdoo has a chance to be a good one. And the process really started the first day the owner watched his offensive coordinator in practice after McAdoo was hired by Coughlin in 2014 to resuscitate Eli Manning’s performance after a 27-interception meltdown in 2013.

“It’s just something about having watched him on the field with the quarterbacks and with the offense,” Mara said. “The first thing that came to mind two years ago was that this guy is a teacher and he’s got an edge to him. He’s not afraid to lose his temper out there and bark at guys, and I happen to like that.”

Beneath Mara’s cool exterior lies a burning, churning chunk of intensity, a man who stews about every loss and is given to an occasional fist bang on the table when things don’t go right on Sundays. The owner is as competitive as his coaches, so he demands plenty from the man who is tasked with leading his team.

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And when he hears it from his unhappy constituents, Mara listens. “I accept my share of the blame for what has gone on,” said Mara, who pointed to an “organizational failure” — not just Coughlin — for the Giants’ three straight losing seasons. “I got a lot of love letters recently from our fans. One of them wrote me and said, ‘The problem with the organization is sitting right in your chair.’ Another one put it a little more succinctly and he said, ‘The fish stinks from the head down.’ ”

Ouch.

“I take that personally and I accept my share. This is all under my watch, and I know we need to get better as an organization,” Mara said. “What gives me confidence is that I know we’ve done it before and I believe we have the right people here to do it again. I believe we can do it under this head coach.”

Mara knows that McAdoo faces a herculean task. He also knows that his coach has little idea of how big the job will be.

“The concern as it always is was that he’s never done it before,” Mara said. “You can say whatever you want, but you just don’t know until he’s out there as the head coach.”

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Case in point: Who figured that McAdoo’s poorly fitting pinstripe suit, which looked about three sizes too big, would become a cause celebre at his introductory news conference? Even McAdoo’s tribute to Coughlin of keeping the clocks five minutes fast at the facility drew plenty of guffaws on social media.

Welcome to the big time, Coach. It’ll only get tougher from here. Just wait until you lose. Especially if you lose a lot.

“This is not a job for the faint of heart, and I’m the right man for the job,” McAdoo said. “I’m hardened, battle-tested, and I’ve been groomed for this opportunity by Super Bowl-winning coaches, players and organizations.”

As those closest to McAdoo suggested, he doesn’t win the news conference. But Mara doesn’t care much about words. The owner wants wins.

“I feel good about him,” he said. “I think he’s got everything it takes to be a successful head coach.”

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He’ll soon find out whether McAdoo will become the next Parcells.

Or the next Arnsparger.