Authorities say when police arrived on the scene located the group of men near Sacramento and Fair avenues just across from the park. Police took three of the suspects into custody without incident. They were later released.
A fourth suspect fled on foot and an officer gave chase. The suspect at one point reached into his waistband and pulled out a gun.
Police say the officer feared for his safety and opened fire, striking the suspect in the leg. Police recovered a gun at the scene a short time later.
The injured suspect was transported to a hospital, where he remains in stable condition. No officers were injured.
St. Louis police Lt. John Green told News 4 he is grateful the woman was brave enough to contact authorities.
"I'm very grateful that she did call the police because a lot of times we don't get cooperation from the community on situations like this," he said. "If it had been somebody else, they may have walked home and never called police, so we're very grateful that she called."