During that game, Severino gave up three hits and two runs in the third inning to put New York in a 3-0 hole.
The Red Sox opened the fourth inning against Severino with back-to-back singles and a walk to load the bases before Boone finally took out his hard-throwing right-hander for Lance Lynn.
"I should've had him out of there," Boone said about Severino. "I sensed he wasn't on top of his game. I felt like they were having a lot of good swings against him."
Boston would explode for seven runs in that inning, putting the game out of reach and leaving the Yankees facing a 2-1 series deficit.
In the decisive fourth game, Boone allowed CC Sabathia to give up three runs on five hits, one walk and one hit by pitch in three innings before pulling the former AL Cy Young winner. The Yankees were defeated 4-3 in Game 4.
Severino's struggles were an ongoing topic throughout the second half. The 24-year-old had a 5.57 ERA with 76 hits allowed in 63 innings after the All-Star break. He posted a 2.31 ERA and allowed just 97 hits in 128.1 innings during the first half.