Al Horford needs to rock if Boston Celtics are to roll in Game 4

* On ESPN: Celtics vs. Cavs, Game 4 (8:30 ET)

CLEVELAND — Marcus Morris nominated himself again as Boston’s lightning rod as the Celtics try to slow the Cleveland Cavaliers’ roll in Game 4 of the Eastern Conference finals on Monday night.

Al Horford, meanwhile, has got to rock.

Rock, as in be there for the Celtics in whatever and however many ways they need him. And they most definitely need him.

Rock, as the steadying veteran presence Horford is, in the eyes of virtually everyone who watches Boston play or has a sense of that roster’s chemistry.

Rock, as in the player his coaches and his teammates lean on precisely at times such as this, regardless of what’s gone on before.

The back story of Horford vs. LeBron James and the Cavaliers in the playoffs is not a pretty one. In four previous encounters — in 2009, 2015 and 2016 while with Atlanta, in 2017 after signing with Boston — Horford’s teams went 1-16. For all of his individual and group success to that point, including four All-Star selections, Horford averaged just 10.9 points and 4.3 rebounds in the four series. He had an average plus/minus of minus-53 per series, according to basketball-reference.com.

The narrative changed as the current East finals began. Horford scored 20 points in less than 28 minutes of Game 1, helping Boston to a blowout victory. Even with Cleveland coach Tyronn Lue tabbing center Tristan Thompson to match up with Horford in Game 2 — Thompson had a history of strong defense against the Celtics veteran — Horford managed 15 points, 10 rebounds, two steals and two blocks as Boston won again. In two games, he shaved 31 points off that negative plus/minus.

This was the Horford people on both sides of the equation, his teams and the other guys, had been lauding for years. Ask any of them about the 6-foot-10 son of former NBA player Tito Horford and you’d wind up with what sounded like blurbs for the back cover of a best seller:

“Al’s important to everything we do,” Celtics coach Brad Stevens said after Game 1. “Every minute of every day, whether it’s the walk-through before, the meeting before, yesterday’s practice, yesterday’s film session. Again, he’s kind of our stabilizer and the guy that we all look to and we take great comfort that he’s on our team.”

James, before the series began, said: “He’s their rock. [He] always is even keel. … He’s been in big games, in big series. If things get chaotic, they know they can always go to Al to do something.”

Cavs shooter Kyle Korver, who became an All-Star himself in 2015 alongside Horford on Atlanta’s 60-22 team, said: “Al is the ultimate teammate. Doesn’t say a lot, so when he says something it means something. … He’s like a Swiss army knife — he does everything. The thing that’s stood out for me in these playoffs is how aggressive he’s been to score … just because he knows the team needs it a little more right now.”

After averaging 12.9 points in the regular season, Horford had upped his scoring to 17.1 through the Celtics’ first 14 playoff games. What he had gone through in the past against James and the Cavaliers seemed to add context and urgency, and a chance for Horford finally to make things right.

Then came Game 3, when Horford took only four shots and scored seven points.

His drop in production was a symptom of what ailed Boston Saturday more than a cause. Thrown by the Cavaliers’ torrid start, the Celtics stopped moving the ball and settled too often for low-reward, pull-up jump shots. Still, without Kyrie Irving, Horford has been the proverbial head of Boston’s snake, so stopping him for the 30 minutes he played made Cleveland’s wire-to-wire rout easier.

“The ball was kind of stagnant last game,” Morris said. “We didn’t get it from side to side. Once we move the ball, we’ll have a better chance of getting him involved more and driving [past] close-outs, things like that.”

While Horford was staying calm and trying to help his younger teammates reconcile their 9-0 home record with their 1-5 road mark, Morris again steered pressure his way by blaming himself for James’ all-around excellence in Game 3. Much as he had on the eve of the series, he embraced the big challenge.

“Personally, I think I did a [garbage] job defensively against LeBron,” Morris said. “He was just too comfortable when I was guarding him. I made myself very vulnerable on screens, and I just wasn’t disciplined, man. We can’t have that in a game of this magnitude, and it showed.

“That [Boston] team we saw [Saturday], I’m 100 percent sure it won’t be the same team on Monday.”

Springing Horford loose to help might matter most.

Steve Aschburner has written about the NBA since 1980. You can e-mail him here, find his archive here and follow him on Twitter.

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