The concert giant Live Nation and its Ticketmaster subsidiary has a harmful monopoly over big concert venues, a Manhattan federal jury has found, dealing the company a loss in a lawsuit over claims brought by dozens of US states.

The jury deliberated for four days before reaching its decision on Wednesday in the closely watched case, which helped peel back the curtain on a business that dominates live entertainment across much of the world.

Live Nation Entertainment owns, operates, controls booking for or has an equity interest in hundreds of venues. Its Ticketmaster booking platform is widely considered to be the world’s largest ticket-seller for live events, from music to sports.

The civil case, initially led by the US federal government, accused Live Nation of using its reach to smother competition – by blocking venues from using multiple ticket sellers or retaliating against them when they did, for example.

“It is time to hold them accountable,” Jeffrey Kessler, an attorney for the states, said in a closing argument, calling Live Nation a “monopolistic bully” that drove up prices for ticket buyers. The jury found that Ticketmaster had overcharged buyers by $1.72 a ticket. The judge still needs to decide total damages.

Live Nation insisted it was not a monopoly, saying that artists, sports teams and venues decide prices and ticketing practices. A company lawyer insisted its size was simply a function of excellence and effort.

“Success is not against the antitrust laws in the United States,” David Marriott, an attorney, said in his summation.

Live Nation has said in a statement that it plans to appeal the ruling. “We remain confident that the ultimate outcome of the States’s case will not be materially different than what is envisioned by the DOJ settlement,” the statement read.

Ticketmaster was established in 1976 and merged with Live Nation in 2010. The company now controls 86% of the market for concerts and 73% of the overall market when sports events are included, according to Kessler. Live Nation noted in its 2023 securities filings that it is the largest live entertainment company, producer of live music concerts and live entertainment ticketing sales and marketing company in the world. Its business brings in over $22bn in yearly revenue.

Ticketmaster has long drawn ire from fans and some artists. Grunge rock titans Pearl Jam battled the business in the 1990s, even filing an anti-monopoly complaint with the US Department of Justice, which declined to bring a case then.

Decades later, the justice department, joined by dozens of states, brought the current lawsuit during Joe Biden’s administration. Days into the trial, Donald Trump’s administration announced it was settling its claims against Live Nation. That agreement required Live Nation to create a $280m settlement fund for states that participated in the lawsuit.

The deal also included a cap on service fees at some amphitheaters, plus some new ticket-selling options for promoters and venues – potentially allowing, but not requiring, them to open doors to Ticketmaster competitors such as SeatGeek or AXS. But the settlement does not force Live Nation to split from Ticketmaster.

A handful of the states joined the settlement. But more than 30 pressed ahead with the trial, saying the federal government had not won enough concessions from Live Nation.

The trial brought the 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 cyber-attack.

The proceedings also aired a Live Nation executive’s internal messages declaring some prices “outrageous”, calling customers “so stupid” and boasting about the company “robbing them blind, baby”.

The executive, Benjamin Baker, apologetically testified that the messages were “very immature and unacceptable”.

The Federal Trade Commission imposed a requirement on Ticketmaster last May to disclose concert ticket fees upfront. In response, the company eliminated a processing fee it would charge at the end of a transaction.

But a Guardian investigation found that Ticketmaster raised other fees to make sure it didn’t lose money. “To account for the loss of order processing revenue, we must adjust fees to offset the revenue loss,” Ticketmaster wrote in an email to the Findlay Toyota Center in Arizona last year.

Former regulators told the Guardian the company may be running afoul of the FTC’s ban on misleading fees. US senators have criticized Ticketmaster for what they see as ignoring consumer protection laws.

“Ticketmaster has taken every opportunity to drive bait-and-switch practices, manipulate the market and drive up the cost of tickets,” said Richard Blumenthal, a Democratic senator from Connecticut.

Associated Press contributed reporting