OAKLAND — It was a spectacular and peculiar sight.

Hundreds — no, thousands — of people pouring off the BART, a full parking lot, tailgates featuring good food, good brews, and good times, and more than 46,000 fans inside the Coliseum, wearing green and yellow, representing every nook and cranny of the East Bay and beyond, all chanting, in full throat “let’s go Oak-land”.

It was fun, it was energetic, it was, sadly, different.

But that made Tuesday’s free-to-attend game was an unequivocal success and the kind of event that can create some serious, positive, momentum for the franchise.

If it did, that momentum couldn’t have come at a better time.

Think of Tuesday’s game as an open house — a chance for the A’s organization to win back fans, and for the fans to see a young, exciting team that’s worth the price of admission.

People love free stuff, and free tickets and free parking is a hell of a deal, but what struck me at the ballpark on Tuesday was how many people were wearing their A’s gear. And this wasn’t new stuff, either — there were a few dusty jackets and hats, but this was well-worn stuff.

Those fans just needed a reason to come out of hibernation — Tuesday was a great excuse.

Perhaps a few dormant fan fires were rekindled on Tuesday. Maybe a few more paying customers were created as well.

It would have been hard to have a bad time at the Coliseum on Tuesday — the A’s players did their job on the field, scoring five runs in the first inning en route to a 10-2 shellacking of the White Sox, and the organization appeared to put on the 50th anniversary celebration event without a hitch.

Tuesday was an encapsulation of the A’s and Oakland at their finest. There’s a ton of potential in this team and in this fanbase.

Put both of them in a new ballpark, and you’d have something special.

I’m telling you, Tuesday was a proof of concept: if you build it, A’s fans will come.

While this A’s team is worth the price of admission, the Coliseum is most certainly not. On Monday, the A’s announced an attendance of 7,479 for the first game of their series against the White Sox. The A’s looked fantastic in that game as well (to be fair, it’s easy to look good against the White Sox), but there had to be fewer than 5,000 people present (the 7,479 number was paid attendance — not the actual number of people who went through the turnstiles).

Monday’s game was the fourth time this season that the A’s have failed to draw 10,000 paying customers to the Coliseum this season. That doesn’t hit A’s owner John Fisher’s pocketbook — per Forbes, the A’s are expected to post $210 million in revenue in 2018 and turn a seven-figure profit thanks in large part to revenue sharing — but it does hurt the team politically. And to build a new ballpark in the Bay Area, you need a lot of money, patience, and community support.

You can’t blame fans for not showing up when there hasn’t been a clear mandate from ownership that the A’s are done being glorified farm team for the rest of baseball. Until then what reason is there to believe that the A’s will be able to keep players like Matt Chapman, Matt Olson, and Sean Manaea around for their arbitration years, much less when they’re free agents? Why should anyone invest their money or time in this team?

But so long as fans don’t show up, it’s going to be difficult for the A’s to get the community support necessary to build the new ballpark that would financially justify to ownership to spend more on payroll.

It’s a paradox that A’s president Dave Kaval needs to break through.

The full house on Tuesday gives Kaval a strong bargaining chip — it’s not hard to massage 46,000-plus showing up to Tuesday’s game into an argument that there’s civic backing for a new park.

“It’s tremendous, I think it bodes well for our future,” Kaval said Tuesday. “You want momentum, you want people excited about your product on and off the field… I think it will help us for the rest of the season, both in drawing fans and the experience here and in our effort with the new ballpark.”

The A’s are currently working on developing two different sites for a new stadium — Howard Terminal and the Coliseum — with the goal of striking a deal to build on one by the end of the year. There are no guarantees with either site, but after the team went all-in on a site near Laney College and failed in embarrassing fashion last year, working both options simultaneously is a prudent plan.

But the A’s can’t wait long to build a new park. Not only does revenue sharing for the team stops in 2020, jeopardizing the team’s profits, which could lead to deeper payroll cuts, there’s also an outside threat.

On Tuesday afternoon, a few hours before first pitch at the Coliseum, the Oregonian’s venerable columnist John Canzano reported that a group in Portland has serious headwind to build a 32,000-seat, privately financed baseball stadium in that city.

They’re not going for a Triple-A club, either.

There’s no indication that Fisher is looking to sell the team or move it at the moment. In fact, everything points to the opposite of that right now: the A’s did just offer to buy the Coliseum site for more than $130 million. (To be fair, while the money offered is substantial, the offer is, inherently, not. Until there’s a deal struck and a check written, the offer is just good public relations.)

But that doesn’t mean things can’t change in the future. The A’s cannot stay in the Coliseum, as is, in the post-revenue-sharing era, but if the A’s cannot build a new ballpark at some point between now and 2019, it might be difficult for Fisher to turn down a free, brand-new home in Portland, or the few billion of dollars that Portland group could offer the A’s owner to buy and relocate the team.

We’re not at that point yet — not by a longshot. But it’s a possibility — one that increased in probability on Tuesday.

The developments up north put more pressure on the A’s to get a shovel in the ground as soon as possible, because I don’t think we’re far from a time when Major League Baseball would be open to relocating the team — it’s no secret that Commissioner Rob Manfred is frustrated with the A’s ballpark quest, and while he has suggested Portland as an expansion site, if the A’s have another setback in their ballpark, don’t put it past him to use a heavy hand with Fisher.

These are critical times for the A’s organization. That’s what made Tuesday’s game so important.

As I saw the Coliseum fill up Tuesday, I wondered to myself if the A’s recluse owner was in attendance — if he would take notice, first-hand, of the strong turnout for the game.

Sure enough, he was. I met him in the A’s dugout during White Sox batting practice.

We didn’t talk for long, perhaps 30 seconds (he was swept away to go to another “thing”), but I can say without equivocation that he was both impressed by the scene and thrilled with the energy in the park.

Given the smile on his face, he must have come away from Tuesday’s game with the same thought I had:

Baseball still works in Oakland, and with the right team and in the right arena, it could thrive once again.