Smith shoved an already airborne Horford in the back with 3:37 remaining in the fourth quarter of the Celtics' 107-94 win on Tuesday night, resulting in a flagrant foul 1 on Smith following a review by the officials.
After the game, Smith said it was a "good call" and that he "blatantly" pushed Horford.
"It wasn't like I was trying to low-bridge him or something to make sure he didn't get it. It was a good, hard foul," Smith said. "I can understand why they gave me a flagrant."
After the shove, Boston's Marcus Smart got in Smith's face, prompting Smith to push the Celtics guard away and leading to technical fouls being called on both players.
Cavaliers coach Tyronn Lue accused Boston of "gooning it up," and the Celtics were OK with that assessment.
"Gooning? That's a good word," Celtics forward Marcus Morris said. "S---, we're doing what it takes. Whatever it takes, every player, 1 to 15, whatever it takes, that's what we're doing. You call it what you want to call it. We're just trying to get the win."