An 18-year-old man has pleaded not guilty to rape charges after allegedly sexually assaulting a 17-year-old girl at Keith Urban's recent performance in Massachusetts.

The alleged assault happened during Urban's concert at the Xfinity Center in Mansfield, Mass. on Saturday (July 26). According to the Sun Chronicle, Sean Murphy of Boston is accused of sexually assaulting a 17-year-old girl at the concert.

According to police, Murphy and the girl first met at the concert, and began kissing at a concession stand before moving to the lawn. Murphy allegedly took the girl by the hand and led her to another area of the lawn, promising to bring her back to her friends. That's where he is accused of sexually assaulting her.

Assistant District Attorney Melissa Tafe says the girl told investigators she only went with Murphy because "she was afraid of what would happen" if she didn't.

Police say several concerned onlookers took cell phone pictures and even video of the incident. Investigators have obtained some of that footage as evidence. The alleged assault came to an end when a woman intervened and asked the girl if she was consenting. When the girl reportedly said no, the woman pulled Murphy off of her. Murphy got up and reportedly tried to elicit a reaction from onlookers before disappearing into the crowd.

An off-duty female police officer tells police she went to investigate and intervene after seeing a large gathering and overhearing a comment about a couple having sex on the lawn. Police sealed the exits to look for a suspect, and arrested Murphy a short time later.

Murphy pleaded innocent in Attleboro District Court to rape charges. He does not deny the encounter, but says it was consensual. The 18-year-old has no previous arrest record. He lives with his parents, who are expected to post the $10,000 bond set for his release.

"Put simply, this was a consensual act, not a sexual assault," Murphy's lawyer said in a statement (via Fox News). "There are no allegations of force or violence against him. This was a private act that regrettably occurred in a public place. Mr. Murphy deeply regrets this incident and I am sure the young woman does as well. The young woman was neither intoxicated nor overcome by drugs at the time. Mr. Murphy has no criminal history whatsoever."

Investigators say both teens were drinking at the concert. As previously reported, 46 people were treated for alcohol-related illnesses at the show, with 22 of them transported to the hospital. More than 50 people were taken into police protective custody at the concert.

In a post to their Facebook page, Mansfield Police are asking anyone who witnessed the incident, or may have photographic or videographic evidence, to contact their Detective Division at  (508) 261-7300. The investigation is being conducted by Det. Sgt. Larry Crosman and Det. Robert Pierce.