Pitching in the eighth inning, Hader recorded just one out, giving up four hits and a go-ahead three run homer to Jean Segura.
Many offensive tweets that included racist and homophobic thoughts from Hader surfaced during the game.
Hader's racist tweets are just the latest to raise questions about whether young athletes should be held responsible for their behavior on social media in the past.
"During last night's game, we became aware of Mr. Hader's unacceptable social media comments in years past and have since been in communication with the Brewers regarding our shared concerns", Major League Baseball said in a statement.
"There's no excuse for what was said or what happened", said Hader, who is now 24 years old.
He added: "As a child, I was immature and obviously said some things that were inexcusable".
Stearns said the Brewers were in contact with Hader, who is "fully aware of the severity of the situation related to his social media comments, regardless of the timeline of his posts".
Teammate Lorenzo Cain called Hader a "great guy", and acknowledged that everyone has "said some insane stuff when we're young".
"When you're 17 years old you make stupid decisions and stupid mistakes", Hader said.
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Hader also tweeted out references to fellatio, and used the n-word in several others, which he said might have come from rap lyrics.
Major League Baseball released a statement about Josh Hader a few minutes ago.
Hader said he plans to talk with his teammates. Cain said he did not ask for an apology and simply wanted to understand the situation before speaking with reporters. Like I said, we'll move on from it.
"There's no excuse for what was said, and, you know, I'm deeply sorry for what I've said and what's been going on", he said.
'We've all said insane stuff growing up, even when we're 17, 18 years old, ' Cain said.
"You live and you learn", he said.
"We move on from it.it is what it is".
Yet, in the following video Hader is asked directly if any of his beliefs have changed from the time he sent the tweets seven years ago to now. "I really don't know exactly what all's out there". So I'm fine. Everybody will be OK. For me, I'm moving on from it.