By the time that John Thompson Jr. and I sat together in the back row of the bleachers at Cambridge Rindge and Latin School outside Boston to watch Patrick Ewing play, we had already known each other for a decade, since he coached St. Anthony’s High and I was a “copy boy” covering some high school games for The Post.

The small, jammed gym was sweltering. But the 6-foot-10, 300-pound Thompson, pouring sweat, came prepared. He had brought a huge bottle of soda, smuggled under his coat in a brown paper bag. Big John leaned back to take a big swig, then stopped suddenly and jammed the bottle and bag down between his legs and under the seats.

“This gym is full of big-time college coaches from all over the country,” said Thompson, as alarmed as if he had just avoided a traffic accident. “If they see me, every one of them is going to tell everybody else that I was drinking out of a brown paper bag. And they won’t say it’s Pepsi.”

That’s one way, one day, I’ll remember Big John, who died at 78 on Sunday: a man aware of every competitive edge or weakness, funny, alert to the world’s manifold sins and wickedness, even as he relished every moment.

As he said the day he made the basketball Hall of Fame: “Not a sip, not a swallow. I want the whole bottle.”

But there were almost as many Big Johns as there were days. Once, my mom said she had enjoyed her late-night talks with that deep-voiced coach who had returned my calls. They had talked about child rearing and any old thing. Which coach? “John Thompson,” she said.

What?!

“Those farm girls are wise,” Thompson informed me, referring to my mother.

Those who refuse to bend to the world as they find it usually end up in one of two ways. The world breaks them. Or, far less often, they bend the world to them. John Thompson bent the world and made it a bit better.

To understand Thompson, it helps to go back a long, long way with him. One Saturday morning more than 45 years ago, John, his two very young sons — John III and Ronnie — and I sat in the living room of Father Raymond Kemp, a priest and lifelong activist for social change.

John had just begun to coach Georgetown University, taking over a program that went 3-23 before he arrived. But he was not interested in discussing his own program, obscure at that time, or its long-shot prospects. He wanted to brainstorm, almost plot, you might say, with Kemp. Thompson wanted to know, at the granular level or as a leader, how he could help effect change.

How do you go from ideas, theory and good intentions to day-after-day impact on the lives of individuals and communities? How do you get Whites — Kemp, who is White, spent 18 years as a pastor at mostly Black parishes — to go beyond “not being racist,” to being part of solutions?

“Money,” Thompson would say. How do you get more of it to people who need it? How do you educate more Black people to be successful, to network and grow in economic influence? Thompson saw Black and White, but he added, “The world is green.”

It is a basic misunderstanding to see Thompson first as a Hall of Fame basketball coach, though he loved his sport and, behind his tough-love facade, adored his teams. Perhaps no man in his sport wanted victory more and trusted it less than Big John, who had seen how pressure to win warped good men. After he won the 1984 NCAA title, he said, “Now I have the period that ends all sentences.”

Before anything else, he saw himself as, and truly was, a catalyst for change who used his national platform to teach and preach social justice.

As a devout Catholic, he saw himself as just as flawed as the next fallen sinner, just as prone to pride or mistakes of judgment. A few times, winning battled with principle as the force that drove him. But I covered his whole career, as a beat writer or columnist, and I can count on my fingers the times principle lost.

Thompson’s pride was the impact he had on his players. And if they didn’t want to receive the full weight of that impact, they could move along — out of Georgetown. The Hoyas’ graduation rate for four-year players was 97 percent, because they knew that, no matter what their academic challenges when they entered, they only had two years to prove they were serious about using school to prepare themselves for life — or give somebody else the chance they were wasting.

Some rival coaches resented that Georgetown, a private school, seemed to design its own socially conscious (and opaque) rules and use them to win a lot of games. I watched for years to see if the ends — in lives changed — justified the means. I think so.

One of his former players, from one of the meanest D.C. neighborhoods, once phoned me at home. He had averaged two points per game at Georgetown. I expected a sob story. Instead, he said he was a broker at EF Hutton and asked if I needed an investment counselor. He left his phone number, told me his financial specialties and said if I ever changed my mind to call.

When 7-foot-2 Dikembe Mutombo was recruited from Kinshasa, Congo, the usual skeptics wondered about his academic credentials. Thompson asked if I wanted to interview him. It was a setup. To my first question, Dikembe answered in four different languages, then, finally, in English, as Thompson split his sides.

For those who knew him well, Thompson was the funniest and friendliest of companions, even in intense conversations. But for 27 years at Georgetown, Thompson was also one of the most disagreeable people in this country. Agreement bored him. Debate invigorated him. Everything he disliked he discussed, with bouquets of exclamation points attached. A cheerful consensus on any issue, especially race, class, money, education or basketball, raised his suspicions.

What John brought to his bully Hilltop pulpit was intense conviction and a streetwise, book-polished way of making his point with a sports-anecdote parable often hidden at its core, like the famous deflated basketball in his office.

A visit to that McDonough Gym office was a graduate course in Big John. First, the door had no name. You thought it might be a stairwell or a storage closet. As you nudged it open, the first glimpse was a shock: an elegant, tastefully under-furnished room with Asian lamps, early American furniture, photo murals of Washington vistas and faint sky-blue walls and rugs.

That door also had no bell. Just as you opened it wide enough to enter, butterfly chimes went off above your head. The surprise made it feel like a gong. Every player noticed and understood — a psychological advantage, an element of surprise, the unexpected. They retaliated with chimes of their own above the training room door, so Thompson couldn’t sneak up on them.

Thompson understood that bookshelves explicate the man. His players couldn’t miss the point: “Winning Through Intimidation.” “You Don’t Have to Be in Who’s Who to Know What’s What.” Machiavelli’s “The Prince.”

Under his desk motto — “To Err Is Human. To Forgive Is Not My Policy” — you’d find “Your Mastery of English” and “The New Etiquette.” Then came Harry S. Truman on how to make things work. Aesop’s fables. “Quotations from Chairman Jesus.” “A Controversy of Poets.” “Ideas and Opinions of Albert Einstein.” And a book of Zen paradox: “If You Meet the Buddha on the Road, Kill Him!”

These days, as America debates serious issues, a serious man will be mourned, a wise man who also happened to be an excellent coach. Thompson’s lifelong friend and former Boston Celtics teammate Bill Russell once said, and Big John repeated, “You should live a life with as few negatives as possible — without acquiescing.”

That is the balance, of radical insights and pragmatic decisions, or anger at injustice and a vow to master the system you want to change, which Thompson achieved.

In seas of grief, amid oceans of memory, we say of those we knew longest and best, “He will be missed.”

But this is more. With John Thompson’s passing, something unique and valuable will be gone. But the essence of the man will remain with all who knew him.

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