CHICAGO (WLS) -- A 23-year-old woman was sexually assaulted in a port-a-potty Sunday night at the Foo Fighters concert at Wrigley Field, Chicago police said.No one was in custody Monday. Police are searching for a 5-feet-9-inches tall man between 40 and 50 years old with brown balding hair.At about 9:30 p.m., the woman was standing in line for food when the man groped her. She left the line and went to a port-a-potty near Gate R and before she could lock the hatch, the man sexually assaulted her.Police are investigating."It was well staffed, they had a lot of people at the doors outside, here, on the street, so as far as that goes that was a safe feeling," said Samatha Walke, who attended Sunday night's concert.Julian Green, a spokesman for the Chicago Cubs, said in a statement: "We were notified of an assault of a female guest and immediately contacted Chicago Police during last night's event at Wrigley Field. We are using every available resource to help authorities identify and apprehend the suspect and are working with CPD to address the matter quickly. We are encouraging anyone who may have information to please contact police."The Cubs also said there are security cameras in the area where the attack occurred, and confirmed they have handed over those tapes to the police to help with the investigation.Monday night, the Foo Fighters played their second Chicago show at Wrigley Field for their Concrete and Gold World Tour.Extra security was in place for the Monday night show, specifically around the port-a-potty areas.Concertgoers that spoke with ABC7 said the incident shed a bad light on what should be a fun event."I think it's just ridiculous that you can't even go to a show anymore without worrying about your life and your livelihood," said Peyton Lessentine, attendee.