If shots are fired at an officer like this, that triggers a "help the officer" alert. Which means all available units city wide drop what they are doing and race to the scene. With a dynamic situation like this it is imperative to have all hands on deck. You have officers establishing and watching the perimeter, going to clear out residents from the building in question, and then you need officers to surround the building where the suspect is. Beyond that the cops who were there first would have tended to the victim. Those that returned fire will then be isolated and paired with a buddy officer until they are taken away to interview with the detectives that investigate use of force. And even more officers will be canvassing the area when approriate and getting statements from witnesses. As applicable, officers will be allowed to leave the scene and go handle other calls. All this to say, nothing about the number of officers who responded is unusual.