American Bridge 21st Century, a super-PAC, released a video Friday calling Brown "hypocritical" for praising the current Red Sox locale, having previously suggesting that the team relocate outside of the city.
Brown released a radio ad last week to mark the centennial celebration, in which he said moving the ballpark would have been a "mistake" and praised the Red Sox owners for improving the stadium "instead of starting over somewhere else."
Brown campaign spokesman Colin Reed told The Boston Globe that in the ad, the senator acknowledges that the calls for moving the team out of Fenway were wrong.
Support of the beloved baseball team became the latest wedge issue in the neck-and-neck senatorial race between Brown and Democratic challenger Elizabeth Warren.
The two political rivals made separate appearances at a taping of "Morning Joe" from Fenway Park on Friday morning, and both of them tried to prove themselves as the best choice for Massachusetts voters. Recent polls have shown the candidates in a virtual dead heat heading into the November general election.
During the MSNBC interview, Warren worked in a dig over Brown's stadium controversy.
"He tried to move the Sox out of Fenway, he's kind of got a problem," Warren said.
Brown wasn't asked about his suggestion of relocation during his own interview, but he did talk about throwing out the first pitch at a Red Sox game.
"I practiced for about two weeks, literally two weeks … walking out there in front of 37,000 people and the guy who was taking me out, he says, 'Hey senator, don't worry if you screw it up, it will be on YouTube for the rest of your life," Brown said.
Brown, who has touted his Red Sox support on the campaign trail, also caused a stir for accepting a donation from a New York Yankees executive. The Boston Herald reported earlier this week that Yankees President Randy Levine donated $2,500 to Brown's reelection campaign last month.
“We’re happy to accept Randy Levine’s donation,” Brown spokesman Reed told the Boston Herald. “The way Scott Brown looks at it is, this is their way of paying us back for Babe Ruth.”
The donation seemed to be taken in stride by both sides of the aisle.
In a separate interview on "Morning Joe," host Willie Geist commented that he was the "lone Yankee fan" on set, to which Sen. John Kerry (D-Mass.) responded, "No, you have Scott Brown there."
The senior Massachusetts senator was quick to make sure viewers knew he was just "playing around."
"I'm just playing around. I'm just hacking around, guys. We're just having fun this morning," he said.
However, the Boston Herald didn't seem sure it would be taken so lightly by voters in the commonwealth.
"The Babe for Brown? Somehow I don’t think Sox fans — even those who love Brown — would take that deal," wrote the publication.