The Atlanta Hawks were unable to keep Al Horford on for another season, leaving the free-agent center to sign a four-year, $113-million contract with the Boston Celtics.

Despite a final five-year, $136 million offer — which was a slightly lower annual number than what other teams offered — it was not give enough for Horford to stay in Atlanta. The promise of a new start with a more stable squad piled up with many other reasons for Horford to walk away.

First, Horford wasn’t satisfied with the reluctant approach that the Hawks took towards offering him the five-year maximum contract that was only available to Atlanta. But he was also not entirely excited to play alongside the center that the Hawks were showing interest in, and eventually signed to replace him.

“He didn’t want to play with Dwight (Howard),” a source told Ken Berger of CBS.

It’s unclear where this lack of interest came from, but some believe it could have to do with the pair’s positional overlap. But regardless of those issues, Horford is mainly ready to play for a more supportive fan base.

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“There wasn’t as much motivation for him when he saw all the empty seats when they were winning,” Horford’s father, Tito, told the Boston Globe’s Adam Himmelsbach. “He said to me, ‘Dad, when we were playing Boston (in the first round of the playoffs), they were down 15 points and they were cheering their team like they were winning the game. They’re so into the game.'”

Along with a more invigorated fan base, Horford will join one of the powerhouse franchises in the NBA. With 17 championships — a record for the league — there’s a lot for the new Celtic to be excited about.

“This is special for us,” said Tito, “especially for him.”

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