The incident, which happened and 91st and Riverside, is under investigation.
Police are searching the park for the suspect. They used extra manpower and even a helicopter to try and find him.
Initially, there was apparently some sort of assault between the officer and the suspect. When that happened, the officer reportedly reached for his gun and began firing. The suspect was not hit. Then, during a scuffle, the officer lost his gun and suffered a minor head injury.
The suspect got away.
Officers arriving on the scene were able to find the gun. However, they are still looking for the suspect.
The off-duty officer described him as wearing a black hoodie with a gold dollar sign printed on the front of it.
Anyone with information is asked to call police.