A teenage girl was raped at same Keith Urban show where 20 people got so drunk they were hospitalized, police said.
The attack happened in front of a large crowd of other concertgoers on the lawn of the Xfinity Center, an outdoor amphitheater in Mansfield, Massachusetts, on Saturday night, a police statement said.
The rape ended when a woman in the crowd pushed the alleged attacker off the victim and he fled, police said.
Sean Murphy, 18, was arrested "a short time later" and charged with rape, police said.
"Officers conducting the investigation were assisted by patrons that had been concerned and took photos and video of the assault on their cellular phones," the Mansfield Police statement said. "Those phones are being processed to recover the digital evidence of the assault."
Urban and his representative did not immediately respond to CNN requests for comment.
The country star and "American Idol" judge posted a video on YouTube after the show Saturday night commenting on what he saw on the lawn from the stage.
"Up on the lawn tonight, that was nutso. It was so cool," he said.
More than 20 people were hospitalized after the concert in eastern Massachusetts, police said. Another 50 were taken into protective custody, and several others were arrested over "alcohol-related issues," local authorities said in a statement.
"In total, Fire and EMS attended to 46 medicals resulting in 22 transports mostly alcohol-related," said Mansfield, Massachusetts, Police Chief Ron Sellon and Fire Chief Neal Boldrighini in a joint statement. "Police dealt with a steady stream of intoxicated persons as well, resulting in over 50 people being taken into protective custody and a number of others arrested for alcohol-related issues."
About 18,000 attended the concert at Xfinity Center in Mansfield, about 30 miles south of Boston.
CNN's Todd Leopold and Cristy Lenz contributed to this report.