An armed man opened the fire on Sunday night in downtown St. Louis near the bush stadium, beating one person in the head and the other in the leg, authorities said.
The authorities did not give a description of the gunman, the report said. The victim hit in the head did not respond, and murder detectives reportedly appeared at the scene, reported the St. Louis Post-Dispatch.
Authorities said both victims are treated in hospital. The victim shot in the head was in a critical, unstable state.
The report said that there was a "chill" event at Budweiser Brew House in Ballpark Village. The event consisted of tickets and invitations. An argument broke out around 8pm. The report states that the two people were considered bystanders.
Maj. Mary Warnecke of St. Louis Police said several hundred were on the roof at the event, reportedly organized on Facebook.
"We have a lot of security in such places, but if someone pulls his weapon … it's very hard to prevent."