Laws vary from state to state, as do the possible penalties. While you do not provide many facts surrounding this incident I will assume the worse. In Michigan where I practice a person who inflicted a serious beating by stomping and kicking someone would almost certainly find themselves charged with Assault With Intent to Murder. This offense in Michigan is called a "capital offense"; this means the possible sentence can be life or any term of years, (I won't get into the whole area of sentencing guidelines which determine the appropriate minimum sentence range the court should consider imposing).
I think curb-stomping with a trip to the ER would qualify in the Assault 3 to Assault 2 range. Depending on the injury caused, the stomper could face some serious prison time. Years. So whoever did the stomping needs to lay low and DONT TELL A SOUL.
This is a difficult question to answer without more information and remember there is often two sides to most stories. One of the first questions is whether or not the action was criminal or justified. One person's act of aggression may very well be seen as an act of self defense For example in many jurisdictions, a person is allowed to use a reasonable amount of force in self defense. Such a reasonable amount of force can even include "deadly force" if necessary to protect themselves from serious bodily injury or death. Should there be a finding of criminal liability, there are many factors that go into sentencing. How serious were the injuries? Is the conviction for an offense that has mandatory minimum time requirements? What is the criminal history of the defendant? Is there any mitigating factors? Was the "victim" armed or the "first aggressor"? Was a limited amount of self-defense proper, but the defendant used "excessive force"? Who is the Judge and what is their sentencing history? All of these factors and more go into predicting the likely sentencing outcome in a case.
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