Kelly received the suspension for his actions in Boston's April 11 game vs. the Yankees when he hit Tyler Austin in the back with a pitch in the top of the seventh inning. The pitch appeared to be retaliation for Austin sliding into second base with high spikes into the leg on Red Sox shortstop Brock Holt in the third inning.
"It's disappointing," said Kelly. "Suspensions are always not fun. We're going to have to play a guy down for six games, so like I said, it's disappointing. It is what it is and I'll get six games, and that's how it goes."
Austin's suspension was reduced from five to four games, it was also announced on Thursday.
Kelly and Austin exchanged several punches before both benches and bullpens rushed to the field. Each player received undisclosed fines in addition to their suspensions for their involvement in the altercation.
"Disappointed, yeah," said Red Sox manager Alex Cora. "We'll manage the game with the guys we have. We've got a good bullpen, so in six days he'll come back and we'll keep rolling."
In 11 games this season, Kelly has a 3.09 ERA and 11 strikeouts in 11 2/3 innings.
While Kelly is out, lefty Brian Johnson and righty Hector Velazquez could get more high-leverage opportunities, Cora said.
Kelly will do what he can to stay sharp during his absence.
"I'll play catch and do all my working out and my running," Kelly said. "I don't have anything scheduled yet for a bullpen [session], but I'm assuming maybe throw one probably two days from now then one more right before, so try to get in two."
Though he didn't get his punishment reduced, Kelly has no regrets about going through the appeal process.
"I always like sticking up for myself," said Kelly. "It kind of helps me sleep at night going in fighting for what I believe in, and it didn't work out."