Smart was fined $25,000 for escalating the altercation by shoving Smith from behind. Smart was assessed a technical foul and ejected with 3:38 remaining in the first quarter of the Cavaliers' 113-102 win.
Smith, who was also assessed a technical foul for shoving Boston forward-center Aron Baynes, was fined $15,000 for initiating the altercation.
Smith and Baynes became entangled in the paint, locking elbows and shoving each other.
Smart then got involved, coming toward Smith and pushing him. While a referee restrained Smith, Smart's teammates Jayson Tatum and Terry Rozier held him back -- or, in the case of Tatum, wrestled Smart to the ground.
Smith made a "chatterbox" motion with his hands, smiling, while Smart appeared to point away as he walked off the court.