But Kyle Seager was the one responsible for knocking Weaver out of the game by getting hit.
Montero hit a three-run homer, and Seager's jawing with Weaver eventually led to the Los Angeles Angels' pitcher being ejected in the Mariners' 3-1 victory on Wednesday night.
Montero's hit his fifth career home run off Weaver, among six hits against the veteran right-hander. But the lasting image was Seager and Weaver exchanging words in the fifth inning, eventually leading to Weaver hitting Seager in the ribs and getting ejected.
Afterward, Seager wasn't backing down from what happened with Weaver.
"It definitely escalated and he handled it the way he wanted to. But from my perspective he quit on his team and I didn't quit on mine," Seager said.
The incident started with Seager calling for time in the batters' box. Weaver (7-11) became impatient, leading to the pair barking back and forth. Following a brief delay, Seager indicated he was ready and Weaver responded with an 83 mph fastball into Seager's ribs. Weaver was immediately ejected by home plate umpire Brian O'Nora.
Weaver said he believed because he was on the pitching rubber and Seager had both feet in the batters' box it was time to pitch.
"Just because he has his hand up doesn't really mean anything. If you're going to do that just step out of the box or keep a foot out or do something," Weaver said. "But when you've got both feet planted and you're looking at me I assume you are ready to go."
It was the second career ejection for Weaver, the previous one coming in 2011.
"If you hit me there it was pretty obvious what was going to happen, he was going to be out of the game," Seager said. "I guess he was tired of pitching."
Montero's fourth homer of the season was a line drive into the bullpen in left field with two outs in the fourth inning. He hadn't faced Weaver since 2012.
"It was right in the middle and he got me out the first at-bat with that same pitch," Montero said.
Hisashi Iwakuma (8-4) allowed one run and struck out a season-high nine in six strong innings to help the Mariners win for the 10th time in 15 games. The loss dropped the Angels five games behind Texas in the AL West, but they remained 3 1/2 games behind Houston in the AL wild-card race.
Iwakuma was lifted after throwing 84 pitches in six innings and allowing just four hits. Iwakuma faced a small jam in the third when Carlos Perez led off with a double and was sacrificed to third. With one out, Murphy hit a grounder to Robinson Cano at second base. Perez broke for the plate on contact and Cano's throw to catcher Jesus Sucre was in time for the out.
Seattle manager Lloyd McClendon said Iwakuma's lower back started to tighten up and was the reason he was lifted after the sixth.
"He kept the ball down, made quality pitches, pitched in when he had to. I thought he was outstanding," McClendon said.
Tom Wilhelmsen pitched the ninth for his 11th save in as many chances.
Mariners: Both McClendon and Iwakuma said there should be no issues with the pitcher making his next start despite the sore back.
Angels: Tommy Milone (8-5) starts on Thursday as the Angels open an important four-game series in Minnesota.
Mariners: After an off-day Seattle opens a three-game series in Texas on Friday with James Paxton making his second start since coming off the disabled list.