Manager Buck Showalter told Hardy that he was getting the day off anyway, but the injury sealed the deal.
Hardy isn't certain of its severity, since he has no previous experience with strained hamstrings.
"I know trainers don't like to hear it, but tweaked something. I have no idea. I've never had a hamstring issue. Couldn't tell you the severity of it. I have no idea," he said.
The injury occurred as Hardy rounded the bases on David Lough's ground rule double.
"Just felt it actually a few times as I was running home," he said.
"Never had this before. When I came back from the back thing, I felt this hamstring was really tight. I don't know if it was from favoring the back or whatever. I've played through a little bit of soreness there since I've come back from the back. Tonight, it just kind of moved a little bit from where I had been playing with it. I don't know how serious it is.
"Yeah, frustrating. Frustrating as hell. It's just seems like one thing after another. And all this has just come up out of no where."
Hardy isn't sure how long he'll be out of the lineup.
"I have no idea if it's a few (days) or what," he said. "If I can jog, it can't be that bad. I've seen guys hurt their hamstrings and can barely walk. I have no idea. I don't know how to describe it.
"(Showalter) told me when I came out that he was planning on giving me tomorrow off anyway and he just wanted to start it early. I don't think I'd play tomorrow. If I have to, I probably could. I kind of wanted to stay in there tonight. If I did, who know? Hindsight is always 20/20, but I guess I could have hurt it worse. I don't know because I haven't dealt with anything like this before."
The game unraveled for the Orioles after Hardy exited the game, with all three errors committed in his absence - the first coming from Ryan Flaherty at short on the controversial transfer rule.
"I was in here getting treatment," Hardy said. "I saw Flaherty catch the ball. Replay showed it. I'm sure you guys all saw it. It's a rule which is going to get changed. I think it's supposed to get changed soon. Someone told me that at the beginning of the series, that they're getting ready to change it.
"Right now, I think it's a stupid rule."