Harrison Bader connects on home run to left-centerfield in third...

Harrison Bader connects on home run to left-centerfield in third inning against Guardians to tie score at 1 on Tuesday, Oct. 11, 2022. Credit: Newsday/J. Conrad Williams Jr.

Harrison Bader didn’t need to imagine what a postseason crowd at Yankee Stadium would be like. He didn’t have to marvel at how the fans who are raucous during a midweek game in August can turn downright feral the minute October hits.

He could just remember. Granted, the vantage point is a little different these days.

Bader grew up 20 minutes away in Bronxville — his favorite player was Roger Maris, he rooted for the Yankees, and he went to playoff games as a fan during their 2009 championship year. But though his innards are all but coated in Yankee pinstripes, his trip to the Bronx hasn’t been a fully magical one — until Tuesday, that is.

“It was everything I expected it could be,” he said. “I prepared myself for it mentally. It’s an atmosphere that I’m very familiar with . . . I obviously haven’t been on the field but I do understand what it means to be successful here, and I do understand the mental side.”

Bader hit a game-tying homer in the Yankees 4-1 win in the ALDS and made a run-saving defensive play, all while friends and family in the stands numbered in the triple digits. All that, from a guy who showed up in August in a walking boot, thanks to his plantar fasciitis — a visual that didn’t exactly play well, considering the Yankees traded away well-liked lefty Jordan Montgomery.

“I think he was aware and had some levity to the situation, like understanding what you said,” Aaron Boone said.

“ ‘We traded a popular teammate and I show up in a walking boot;' he kind of made light of that. But we also knew we were getting a really good player.”

First, the defensive play in the third: With one out, Amed Rosario on first and a run already in, Jose Ramirez hit a double to the gap that, in any other universe, would score the Guardians speedy shortstop. But Bader, one of the best defensive outfielders in baseball, and among the fastest, too, cut off the ball to keep Rosario at bay.

In the bottom of the inning, Bader tied the game in his first at-bat — hitting Cal Quantrill’s full-count sinker 406-feet to left. He’s the first player in Yankees history to have his first home run with the team come in the playoffs.

In all, it’s proved to be a quick shift in narrative for Bader, whose injury meant he didn’t play until Sept. 20. Meanwhile, Montgomery — whom many believed the Yankees should have retained for rotation depth — was thriving in St. Louis. In his first seven games with the Cardinals, he went 5-0 with a 2.28 ERA. But as Bader worked toward his return, Montgomery began to regress — pitching to a 6.64 ERA in his final four starts. He was left off the Cardinals Wild Card roster before they were eliminated.

“I do truly like to play the game emotionless,” Bader said. “It’s very easy to be distracted on wanting to be a hero, wanting to hit a big home run, wanting to go out and do something. And, quite frankly, in my experience . . . not letting the game come to you will get you into trouble.”

Bader did plenty of that, and in the process, cemented his trade deadline’s most important reversal: Where Montgomery was pitching in August while Bader was idle, Tuesday, Bader was rounding the bases at his hometown ballpark while Montgomery’s season was over.

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