Seven years and one week ago, Ryan Mountcastle and Austin Hays became teammates.

Hays had just turned 21 years old and was tearing his way through the minor leagues, unknowingly approaching his MLB debut for the Orioles later that season. Mountcastle was 20, a year removed from being drafted in the first round, when he was promoted to Double-A Bowie on July 20, 2017.

The pair has spent the vast majority of the 2,563 days since as teammates. Until now.

“It sucks,” Mountcastle said. “But it’s sort of the nature of the game.”

Hays, a pivotal piece since the rebuild began in 2019, was traded Friday to the Philadelphia Phillies — a surprising and unconventional deal between two of baseball’s best clubs. The trade brought back a potential high-leverage reliever in Seranthony Domínguez, but gone is one of Baltimore’s team leaders.

“I played with him for what seems like 10 years now,” Mountcastle said. “Really good friend, really good teammate, good father and a great dude in general. It’s never easy, but I wish him the best of luck over there in Philly.”

Hays was one of the last vestiges of a bygone era. He and Anthony Santander were the lone players who connected the pre-rebuild Orioles to the current iteration. Hays’ call-up in September 2017 — 15 months after he was drafted by Baltimore in 2016’s third round — was a last-ditch effort by a struggling team to make a late push for the postseason. Santander debuted that year, too, and opened the 2018 season in the majors, a few months before the team initiated the rebuild by selling at the deadline. Hays was then part of a core that survived the treacherous rebuild, trudging through a three-season stretch during which the Orioles were one of the worst teams in baseball with 108 losses in 2019 and 110 more two years later. Cedric Mullins debuted in 2019 and Mountcastle in 2020, forming a quartet that experienced the lowest of lows before the success in recent years.

As the team emerged as a contender in 2022, established itself as one of baseball’s best teams with 101 wins last year and continued that success into 2024, the painful memories of the past were never gone from their minds. That was especially true for Hays, who went from playing alongside Adam Jones under Buck Showalter in 2017 to losing 19 straight games in 2021 to winning the American League East in 2023.

Heston Kjerstad, previously the other half of Hays’ platoon this year and now perhaps his full-time replacement in left field, said the 29-year-old outfielder made sure to remind the Orioles’ young core — the players drafted as a result of the rebuild Hays endured — that winning seasons are not guaranteed.

“He would always make sure you appreciated that you’d come into this team and it’s a winning team because it wasn’t always that way,” Kjerstad said. “He made sure to put it in perspective so that way you know what you’re coming into and also, ‘Better keep playing like this because you don’t want to be on the other end.’”

Veteran James McCann joined Baltimore last year, but as an 11-year veteran, he could tell the role Hays played in setting the standard for the Orioles’ young players.

“He’s a grinder. Something we talk about in here is the way we go about our business, the way that we focus on the process, we grind,” McCann said. “He fits that mentality and was part of that culture being built here.”

Jordan Westburg, a second-year player whose even-keeled demeanor and intense approach have defined his early career, agreed that Hays’ style of play exemplified the way the Orioles play.

“I think he embodied what we try to be about as an organization and as a team,” Westburg said. “Just gritty, determined, head down, push through whatever’s coming his way kind of ballplayer.”

Ramón Urías wasn’t a homegrown player like the others, but he joined Baltimore in 2020 and slogged through the 2021 campaign alongside Hays. Urías, whose status with the Orioles is uncertain with prospects in Triple-A banging on the door, said a trade involving Hays “didn’t surprise me at all.”

But losing a mainstay like Hays still had an impact on Urías.

“It definitely hurt because he was part of our family here,” Urías said. “A special guy with a lot of talent, a true professional. We’re going to miss him, for sure.”

Since he was hired before the 2019 season, manager Brandon Hyde watched Hays go from a promising prospect to an injury-prone outfielder to a Gold Glove finalist and an All-Star last year. Hays’ role diminished this year as he struggled in April and landed on the injured list, but he’s crushed left-handed pitching since he got healthy, leaving a hole for Baltimore to replace against southpaws.

One of Hyde’s go-to phrases is to call a player a “true pro,” and he invoked it when talking about Hays on Friday. Throughout the 2022 and 2023 campaigns, Hays played through several injuries that Hyde has said would normally land a player on the shelf.

“Nobody played harder. Nobody played more hurt,” the sixth-year skipper said. “To lose someone like that that we’re all close to, it’s tough. Close friends for a lot of guys in that clubhouse and we definitely wish him well.”

Hyde said his favorite memory from managing Hays was telling him he was starting the All-Star Game and watching him take his place in center field at the Midsummer Classic.

“To be the one to call him that day, to let him know he’s starting the All-Star game, that was a special moment,” Hyde said.

Like Hays, Hyde suffered through those rebuilding years, too — writing out lineup cards that had little chance of winning, playing with barely any fans in the stands, watching his club lose 19 straight games in 2021.

To say goodbye to a player who went through all that with him, Hyde said, is “never easy.”

“But it’s also part of the game and part of the business of professional sports,” Hyde said. “You give a guy a hug and shake a guy’s hand who you’ve been with for a long time and you hope that you get a chance to manage him again because he’s been an absolute pleasure to be with every day for quite a few years.”

The trade made sense for the Phillies and Orioles given the former’s bullpen depth and need of an outfielder and the latter’s inverse. But that doesn’t mean it didn’t send ripples of shock through some in the Orioles’ clubhouse, even veterans who know how crazy this time of year can be with Tuesday’s 6 p.m. trade deadline just days away.

“It’s definitely surprising. Definitely surprising,” veteran Ryan O’Hearn said. “We have all these highly touted prospects, but it’s hard not to see the rumors come out about guys and stuff like that.”

For O’Hearn, McCann and many others in the Orioles’ clubhouse, losing Hays was more about seeing a friend you spent more than 80 hours a week with than a player with a .255 batting average and a .711 OPS.

“The human aspect of it is probably more real for us than a lot of people understand, but we also understand that it is a business and things change quickly in this game,” O’Hearn said. “But, yeah, obviously, I love Austin Hays, and I’ve enjoyed playing with him. I hope the best for him and his family moving forward.”

McCann’s twin boys, Christian and Kane, reacted like any 6-year-olds would to the news: “Oh, no Levi and Hayden are going to be gone,” McCann recalled his sons saying about their friends and Hays’ kids.

“That’s something a lot of people don’t understand is those relationships that are built from a family standpoint,” he said. “That’s the tough part about this game.”

Hays was far from the only leader in the Orioles’ clubhouse, and as the club scuffles amid a 12-17 stretch since June 21 — its worst skid in more than two calendar years — they’ll need to step up even more in Hays’ stead.

O’Hearn said there’s no “blueprint for how to move forward” other than to approach the remaining 59 games the same way as always.

“Austin was definitely a leader, we have other leaders as well,” O’Hearn said. “We just keep going. That’s how the game is, how the business is.

“We still have a goal that we’re trying to accomplish.”

Baltimore Sun reporter Matt Weyrich contributed to this article.