LOS ANGELES — Watching your children grow up is an exercise in the acceptance of mystery.

When your kids are little, you know everything about them. Babies don’t keep secrets. Toddlers don’t harbor interior lives. But slowly and then quickly, children turn into teenagers, and teenagers are strangers even to themselves. The babies whose hair you can still smell when you close your eyes become their own private universes, both self-contained and limitless.

My boys are 17 and 15, which means I don’t know much of anything anymore, especially about them.

Charley, my oldest, has autism, and so he always has stood some version of apart, his true feelings obscured by his scripting and passion for books and trains.

Sammy has been easier to parse because he’s a new and improved edition of me. For years I could look at him and know exactly what he was thinking, because that’s what I was thinking, too.

– Stream on ESPN+: LaLiga, Bundesliga, more (U.S.)

Mostly, we were thinking about soccer.

The game has been our shared obsession since his first word was “ball.” I’ve been his coach for more than a decade, and these days he’s also one of my assistants when I referee, and together we’ve watched hundreds of games, our Saturday mornings carved out seasons in advance: Liverpool at home to Man City, Burnley away to Wolves.

Now other affections have started to creep into his expanding mix, and more grown-up desires and worries have arrived with them.

We’ve agreed that next season he’ll play under a new coach, because he needs and probably wants someone else to take him from here. And I know it won’t be long before I’ll be spending my Saturday mornings alone.

I’ve told myself that such departures are the natural order of things, and there remains no shortage of love between us.

It still hurts to watch him take his leave.

The instant Lionel Messi announced he was coming to Inter Miami, I made a snap decision: I’d do whatever it took to watch him with Sammy. I can’t articulate why, exactly, beyond the guarantee of 90 precious minutes with my son when time feels like it’s moving faster than ever. Messi-mania has swept America, but my strain of it wasn’t really about Messi at all.

I looked at Miami’s schedule and put a pin in its away game against LAFC on Sept. 3, maybe so that I could pretend we’d be saying goodbye only to summer. I scored two seats in the front row of the North Stand, at the bottom of the 3252, LAFC’s army of ultras. “How?” Sammy asked when I told him we were going. It was too hard to explain that a father fighting to keep his grip on his son is a formidable opponent to reason.

We spent a couple of fantastic days together in L.A., and then Sunday came. That morning, Sammy and I spent hours getting thrashed by the surf in Santa Monica.

Now we found ourselves at the bottom of a different kind of surge in the shadow of downtown.

“When we score,” a kid dressed in black behind us said, “cover your heads.”

Messi took the field, a little duck-footed man dressed in pink, and I leaned into Sammy and pointed at him the way I’d dreamed I might. Sammy did me a great favor and nodded as though he didn’t already know what I wanted to teach him.

Then the whistle blew. Outwardly, at least, the 3252 was unmoved by the presence of the greatest football player the world has ever seen. The group beat its drums and waved its flags and sang its songs and threw its insults unabated.

The rest of the supposedly home crowd didn’t bother hiding their love and wonder, rising and falling with Messi’s every move the way the tides follow the fancies of the moon.

The casuals and celebrities in attendance — Prince Harry! Leonardo DiCaprio! Selena Gomez! — were almost hilariously single-minded in their viewing, never mind the adjacent near-greatness of Sergio Busquets and Jordi Alba. It was like watching tourists at the Louvre flock toward the Mona Lisa, ignorant to The Raft of the Medusa and Liberty Leading the People waiting just over there.

Regarding Messi in the flesh for the first time is disquieting in its way, even absent the strange attention vacuum he creates. Initiates expect an unbroken string of brilliance.

Instead, he can look lost for long stretches of the game, wandering around like a man in a food court who’s not quite sure what he wants for lunch. Then he sees the play break through his singular lens, and suddenly he’s at the top of the box, poised to make something out of nothing.

Messi missed a couple of early chances, giving LAFC goalkeeper John McCarthy a story to tell his grandchildren one day. (McCarthy later got Messi’s shirt as proof.)

He never did score. He still did Messi things.

“How did he know that guy was there?” Sammy asked me after one sublime switch, and I can’t tell you how happy that made me. My teenage son was leaning into me again, excited, chatty, engaged. When he took out his phone, it was only to take pictures. He was lit up like a kid.

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Messi lays off pass to Campana who scores Inter Miami’s third goal

Lionel Messi lays off a nice pass to Leonardo Campana who finishes off Inter Miami’s third goal.

I watched the clock and willed it to slow down. Halftime came in what felt like seconds. By then, Messi had already celebrated an Inter Miami goal in front of our eyes.

Later, he assisted two more. The first delivery, to an invisible Alba, felt like the sort of moment that demanded a plaque immediately be set in the grass.

“Messi! Messi! Messi!” the crowd chanted.

LAFC snatched one back at the death. It had taken so long, Sammy and I forgot to cover our heads. We turned to watch the 3252 erupt. A foamy cascade of beer poured down on us, enough for a smiling Sammy to catch a mouthful.

“Your first beer!” I laughed.

“No, pops,” he said.

Oh.

That is how things will go between us from now on. That is a fact.

But it is also a fact that one Sunday in September, way back in 2023, Sammy and I swam in the ocean and then watched Lionel Messi play. Whatever else happens between us, however our orbits change and diverge, those things will have happened, too. If we share nothing else, we will share those memories, and we will share them forever.

The final whistle blew.

“You enjoy that?” I asked Sammy. He nodded and gave me a hug. “Good,” I said. “Me, too.”

We watched the players walk off the field. The rest of the stadium emptied. My son and I stood together and looked out at the grass, under the last of the lights, at the end of a blessed night in Los Angeles. Finally, I moved to go.

“Can we stay a little longer?” Sammy asked.

I looked at my boy and marveled.

Suddenly there he was, all grown up. There he was, the one who didn’t want to leave.