Law enforcement is in a precarious position. They have the main duty of protecting the public and maintaining law and order. At the same time, they have to be careful to not violate civil rights or make judgment calls that break the law. This is not always an easy thing to do, but the law tries to define how law enforcement may act when taking you into custody. This includes how New York defines excessive force.
The New York City Department of Investigation explains excessive force or police brutality is when an officer goes beyond what is reasonable to subdue or capture a suspect. It is an expectation of the public that officers will use force when arresting or capturing suspects, but excessive force goes beyond what is normal or needed. This is a concern when fatal force comes into play.
In such situations where someone suggests excessive force occurred, it usually ends up in a court. It is up to the court to determine on a case by case basis whether force is excessive. This is general how these cases go because the law does not offer a black and white definition of excessive force.
There is a move to call something excessive if the officer did not try to first deescalate the situation or try an alternative to the use of force. This does require more training for officers to learn the skills and to give them the tools they need to try alternative options first while also not putting their lives or the lives of the public at risk. This information is for education and is not legal advice.