For decades, HBO was the preeminent television brand in boxing. The highest-rated fight in its history, a heavyweight title match between Mike Tyson and Frank Bruno on Feb. 25, 1989, did a 35.7 household rating, meaning more than a third of its subscribers watched that fight.

It’s difficult for anyone who remembers HBO’s dominance in that era to reconcile its announcement Thursday that it is exiting the live boxing business.

It’s like the New York Yankees announcing they are giving up on baseball.

This, though, was not an overnight decision. The seeds were planted nearly 20 years ago, when HBO Sports president Seth Abraham and his chief deputy, Lou DiBella, left the company.

HBO’s dominance slipped perceptibly year by year after that, to the point where on Thursday, Peter Nelson, Abraham’s linear successor, cited research data to explain boxing’s demise on the network.

“It’s nothing mysterious,” said Nelson, the executive vice president of sports at HBO. “We’ve had consistent audience research that indicates boxing was no longer a factor for our subscribers.”

HBO in 2018 is “Ballers” and “Last Week Tonight with John Oliver” — no longer Floyd Mayweather versus Jose Luis Castillo or Aaron Pryor versus Alexis Arguello.

For years, the president of HBO Sports was among the three or four most powerful persons in boxing. But there was a slow, precipitous decline over the past several years, to the point where earlier this month, archrival Showtime nearly doubled HBO in ratings when the networks went head-to-head with boxing.

DiBella left the network and became an elite promoter, but nearly 20 years after his departure, he’s still closely associated with the network. He created its “Boxing After Dark” series that featured younger fighters and fighters in weight classes that HBO’s “World Championship Boxing” franchise largely did not cover.

It was an emotional day for DiBella as he processed the news.

“I’m not going to lie and say there isn’t a degree of personal pain, because there is,” DiBella said. “Very much so. It hurts to watch a proud franchise that had an historic legacy and the one-time biggest brand in boxing crumble by its own hand and decision-making.”

That was a none-too-subtle jab at HBO’s current leadership, but HBO’s decision is representative in a lot of ways of the shift in viewership.

Top Rank’s Todd duBoef railed for years about the perils of premium cable network for boxing. HBO and Showtime dominated the industry since the 1980s but had vastly smaller audiences than the over-the-air and basic cable networks, so boxing’s best programming was always shown to the smallest amount of viewers.

It’s what duBoef has cited repeatedly for his decision to part ways with HBO in 2017 and give his vertical to ESPN.

“HBO had fighters like Sugar Ray Leonard and Muhammad Ali and [Marvelous Marvin] Hagler and [Thomas] Hearns, who were all developed elsewhere and then came to fight their biggest fights on their network,” duBoef said. “Basically, they took a product at the top, that was developed elsewhere, and they showed that and it worked. They’re not a development platform. HBO is about big events and big stars and they weren’t into being a developmental platform. But when other networks began to make a play into the [boxing] business, their big-event model became a developmental model and they had to take young prospects and start to develop them. It was not their purpose.

“You’ve heard me talk a lot about the fact that to us, the combination of the whole vertical was the big play. So, if a [promoter] gave an ESPN or a Fox or an NBC, whoever it was, its boxing business, it was getting the preseason and the regular season and the playoffs and then the finals. HBO never came up with a solution for the preseason and the regular season. They relied on others to do it and they’d come in and grab the finals. So now, when a media partner has the entire vertical, it looks like a different sport.”

ESPN is doing for Top Rank, and Fox will begin in December doing for the Premier Boxing Champions, what HBO never really could do: They’ll put boxing front and center and not only broadcast top-end fights, but they’ll do pregame and postgame shows and studio shows and air all levels of matches.

It enables boxing to be viewed as other professional sports are. The NBA wouldn’t be nearly as popular as it is now if during the regular season, only a handful of marquee games were televised and the Finals were the big deal. The NFL clearly relies on shows like ESPN’s “Primetime” to help build and maintain interest.

Because of the nature of the subscription-selling business, that doesn’t make sense for a premium cable channel like HBO.

HBO learned that when it had a hit series like “The Sopranos” or “Game of Thrones,” it could make money off merchandising and in syndication and in ways that it never could from boxing.

“Today, there is so much content out there and we’re all being challenged [with] cord-cutters and content online and content through their phones, and things like that,” duBoef said. “When they started in the ’70s, there were three networks. So they took a product that had been on network television, overpaid and put it on a smaller platform. They could move the needle and people would go get it and subscribe.

“You’re dealing with the entire landscape of media now. There are so many options for someone now, and HBO is competing with Netflix and Hulu and all these guys that have $11 billion budgets. When they do a series, they own it worldwide. They own it and market it and can sell it to all of their platforms globally. Boxing is an event-based model and they don’t own anything. It’s one night and that’s it.”

Nelson said HBO is open to broadcasting fights through the end of the year and that the IBF middleweight title fight between Daniel Jacobs and Sergiy Derevyanchenko on Oct. 27 isn’t its last bout.

HBO was a boon for boxing, coming in at a time of transition for the sport. When the broadcast networks began to shy away from boxing following Duk Koo Kim’s death as a result of injuries suffered in the ring during a 1982 fight on CBS with Ray Mancini, HBO was there to pick up the slack.

Showtime came along a few years later, and between them the overwhelming majority of megafights in the 35 years since aired on one of those networks.

HBO was a good steward of boxing for much of its time, but its time has come.

It was a great run, but it was clearly time for an amicable parting of the ways.

Boxing will survive, and HBO will, too.

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