It was also reported that members of Hader's family in attendance at the game had changed their shirts to blank National League gear after being told of the developing scandal.
As Hader pitched in the game Tuesday in Washington, D.C., Twitter users retweeted posts from his past that contained racist, homophobic and misogynistic comments.
Asked if he was anxious about facing discipline, the 24-year-old said he would live with it.
"I don't remember too far back then", he said.
Hader was asked about the tweets after the game, and said he was "young, immature, and stupid".
"Being 17 years old, you make stupid decisions and mistakes", he said.
Warning: these tweets that Hader sent out are extremely offensive.
It will certainly be interesting to hear MLB's response, and hopefully it's not just that Hader was a dumb 17-year-old.
Several of Hader's teammates spoke out in support of him on Tuesday after the game, including outfielder Lorenzo Cain, who is African-American. "He's young. We all say some insane stuff when we're young. You always in trouble for things you said when you're younger", Cain added. This mistake won't happen again'. "We'll move on from it". "I'm moving on from it individually, anyway". MLB attempting some sort of way-after-the-fact punitive action on Hader like a fine or a suspension would (a) be met with some understandable resistance by Hader and the union; and (b) would look more like the league trying to deal with a P.R. crisis more than dealing with the player. The situation is what it is. I know Hader. He is a great guy. Like I said, we'll move on from it. He made his major league debut in June 2017.
Deputy Commissioner Dan Halem, speaking outside the NL clubhouse, said he had spoken to Hader.
Hader was willing to accept any consequences that could come in the future. The first-time All-Star selection threw multiple pitches in the dirt or high out of the strike zone.