NEW YORK — A jury has found that concert giant Live Nation and its Ticketmaster subsidiary had a harmful monopoly over big concert venues, dealing the company a loss in a lawsuit over claims brought by dozens of U.S. states and the District of Columbia.

A Manhattan federal jury deliberated for four days before reaching its decision Wednesday in the closely watched case, which gave fans the equivalent of a backstage pass to a business that dominates live entertainment in the U.S. and beyond.

“It’s a great day for antitrust law,” a jubilant attorney, Jeffrey Kessler, said as he emerged from the courthouse.

Earlier, the judge told lawyers on both sides to meet with one another “and the United States” to provide a joint letter proposing a schedule for motions and how the remedies phase of the case would occur. He told them to deliver it by late next week.

The trial brought Live Nation CEO Michael Rapino to the witness stand, where he was questioned about matters including the company’s Taylor Swift ticket debacle in 2022. Rapino blamed a cyberattack.

The proceedings also aired a Live Nation employee’s internal messages to another employee declaring some prices “outrageous,” calling customers “so stupid” and boasting that the company was “robbing them blind, baby.” The employee, Benjamin Baker, who has since been promoted to a position as a ticketing executive, apologetically testified that the messages were “very immature and unacceptable.”

Live Nation Entertainment owns, operates, controls booking for or has an equity interest in hundreds of venues. Its subsidiary Ticketmaster is widely considered to be the world’s largest ticket-seller for live events. Its lawyers did not immediately comment as they left the courthouse, but said a statement would be issued shortly.

The verdict could cost Live Nation and Ticketmaster hundreds of millions of dollars, just for the $1.72 per ticket that the jury found Ticketmaster had overcharged consumers in 22 states. The companies could also be assessed penalties. In addition, sanctions could result in court orders that they divest themselves of some entities, including venues such as amphitheaters that they own.