Porcello allowed six runs on nine hits and one walk, striking out seven in 5⅔ innings before leaving with a 6-2 deficit against the Tampa Bay Rays. He proceeded to smash two TV monitors in the dugout as he headed to the locker room.
"I kind of wish I did that without cameras being on me,'' he said after the Red Sox's 8-5 loss. "I apologize to everyone that had to see that. It's not a behavior that I feel like is representative to me and my personality. The frustration got the best of me.''
Porcello, the 2016 AL Cy Young Award winner, was the beneficiary of the best run support in the majors in his previous four starts, with the Red Sox scoring 49 runs while he was in the game. He was 4-0 in those starts, despite allowing 19 runs in 22⅔ innings.
Porcello is 9-8 with a 5.74 ERA this season.
The Associated Press contributed to this report.