Dave Gettleman has a plan. He has to have a plan, right?

Exactly what is that plan?

Chasing a Super Bowl with a 38-year-old Eli Manning, who counts $23.2 million against the cap, and letting a 25-year-old co-captain and three-time Pro Bowl safety walk out the door for nothing in return, on a defense already sorely lacking in playmakers, pulls the rug out from under Giants fans who were right to plead BETTER SAFETY THAN SORRY.

Hitting the pause button on a potential five-year, $60 million deal is one thing. Refusing to commit to one of your own, one of your homegrown stars, for one lousy season on the franchise tag, sends the worst possible message to the locker room, to Giants fans, to the rest of the league.

Shame on the Giants.

Casey Stengel would have said, “Can’t anybody here play this game?”

Gettleman has vowed to (re)build the Giants one brick at a time, but the foundation of his house isn’t nearly as sturdy today without a brick such as Collins entering his prime.

We can debate whether a player who has been more box safety than interception machine is worth $11.15 million on the franchise tag, because most teams, especially the Giants, value a pass-rusher and cornerback more.

We can’t debate whether it is bad business collecting assets during last October’s impromptu fire sale for “Snacks” Harrison and Eli Apple but allowing a more marketable talent to venture out freely into free agency without attempting to reach a belated deal with him. Because it sure is.

Especially when Gettleman could have traded Collins at the trade deadline last season for a mid-round pick. Which Gettleman could use because he opted to spend a third-round pick on cornerback Sam Beal in the 2018 supplemental draft. The Giants now have to wait until 2020 for a potential compensatory pick on Collins.

So this is the day when Quarterback Hell met Salary Cap Hell at 1925 Giants Drive.

March Madness.

And for much of the fan base who treasured Collins’ swagger and commitment, March Sadness.

One of Gettleman’s mantras when he made Odell Beckham Jr. the $95 Million Man was, “You don’t give up on talent,” but that is precisely what he is doing here, because he somehow found himself cash-strapped between the Rock of Gibraltar and a hard place, with no escape route.

In the span of 14 months, Gettleman and the Giants have gone from Let’s Win Now (Manning, Nate Solder, Alec Ogletree, Saquon Barkley) to Ahh, The Hell With It once they realized the oasis in the Big Blue desert was a mirage.

Fear of a sit-down strike distraction by Collins through the summer should not and could not have motivated Gettleman as much as him possibly viewing Collins as a square peg in a round hole on James Bettcher’s defense — except this was a 100-tackle-a-season square peg with leadership, intangibles and athletic arrogance.

No one will confuse Collins with Lawrence Taylor, but his departure will leave yet another void on a defense that now needs a pass-rusher or two (O Romeo, Romeo, wherefore art thou, Romeo Okwara?) should Olivier Vernon follow Collins out the door. A cornerback, two safeties, maybe a linebacker and a partridge in a pear tree.

Only two years ago, before the injury bug began to bite him a bit, Collins finished third in the Defensive Player of the Year race. And still he insisted on playing on a sprained ankle during the 2017 nightmare, when most players would have shut it down.

Gettleman seems to have aced the 2018 draft, but he still needs to find his franchise quarterback, in case you haven’t heard. Which means Giants fans will need him to be George Young or Ernie Accorsi and complete what looms even more now as a Hail Mary to get the Giants back in the game.

“I want to retire a Giant,” Collins said at a Thuzio Q&A last year. “My biggest thing was, whoever I was drafted to, was where I wanted to finish. My all-time goal is to finish as a Giant.”

The Giants traded their 40th pick and fourth- and seventh-round picks to the Titans to move to the top of the second round of the 2014 draft for Collins, who was stung that he fell out of the first round and vowed to carry a chip on his shoulder. Big, tough, smart and versatile.

“They missed out on a good player,” then-GM Jerry Reese said.

Reese missed out on too many picks. He got this one right. Whatever Collins has left in his locker, he doesn’t need anymore. Tag you’re not it, Landon Collins.