On the facts stated here it is impossible to say. We would need to know what the person was charged with have they any previous.were any injuries serious.Penalties can range from conditional discharge to community service, fines and even prison for the varying degrees of assault but it all depends on the circumstances and I'm afraid your facts dont give any clues.
Suggest your boyfriend contacts the officer dealing with the offence and ask him for advice.
In any event your boyfriend should be informed of the outcome after the court appearance.