The Chicago Cubs had just swept the San Francisco Giants for the first time in nearly 40 years, but a bomb threat didn’t give them any time to celebrate. Shortly after the Cubs won, 2-0, to beat the defending World Series champs for a fourth straight game, the threat compelled police to bring in bomb-sniffing dogs and clear out more than 39,000 fans, media members and stadium employees. 

The threat appears to have been an empty one: Stadium employees and media were allowed back inside the stadium about an hour later. A Chicago police spokesman declined to offer further details on the threat or who called it in.

Sunday’s incident is the first of its kind at a Major League Baseball park this season, and the first since MLB enacted new security procedures and protocols for its stadiums in 2014, in response to the Boston Marathon bombings of April 2013 that left three people dead and 264 injured. Among other things, every MLB club must screen fans through a metal detector before they enter ballparks for games. In 2013, the National Football League instituted a number of policies intended to improve security at its stadiums as well. 

Earlier this year, a man phoned in a bomb threat in Jamestown, New York, before a home game of the minor league Jamestown Jammers. The suspect was arrested and currently faces a felony terrorism charge.

A protected Chicago Landmark, Wrigley Field is different from many other MLB stadiums because of its location in a densely populated neighborhood, where it is surrounded by busy bars and restaurants. The stadium recently completed the first of a four-part series of renovations, a plan that has drawn the ire of some purists but has received passing grades from architects and many baseball fans. 

The Cubs, a season-high 14 games over .500, trail the National League Central Division-leading St. Louis Cardinals by 8.5 games. The Giants, at 59-52, sit 3.5 games behind the Los Angeles Dodgers in the NL West.