The preliminary hearing was held today for the two men accused of beating Giants fan Bryan Stow at the Dodgers’ season opener last year. The two men, 30 and 31, face felony charges of mayhem and assault and battery resulting in serious bodily injury, along with federal weapons offenses not related to the incident.

Dismayingly, another fight occurred outside Dodger Stadium last week. One man was sent to the hospital, just as Bryan Stow was. Four people were arrested on suspicion of assault with a deadly weapon, but they have not been charged. The Los Angeles City Attorney’s Office, which is prosecuting that case, has decided the four will not face felony charges, although they may still be charged with misdemeanor battery.

How do prosecutors decide what criminal charges to file after an alleged assault, beating, bar fight or similar incident? That interesting question was addressed on Southern California Public Radio’s news blog recently, and it may come as a surprise to many people to learn that much of that decision is based on the prosecutor’s own sense of how serious the assault or battery actually was.

“If Mike Tyson punches someone in the face, that’s probably a felony,” says Loyola Law criminal law and procedure professor Stan Goldman. “I’m 126 pounds. If I punch someone in the face, I might bust their lip, but I’m probably not going to do much damage,” he says. “If I do it, it’s probably battery.”

Goldman explained that prosecutors are more likely to charge assault and battery as a felony if the injuries involved are serious, such as broken bones. Cuts and bruises are more likely to result in misdemeanor charges, under ordinary circumstances.

Intent also counts — if it can be proved that the assailant was attempting to cause great bodily injury or to murder the other person, he or she might be charged with a felony, even if they failed to cause much actual harm.

In a fight, the person who threw the first punch is typically charged — with either misdemeanor or felony assault or battery, as appropriate. The person who responded with a punch of his own is usually considered to have acted in self-defense, and prosecutors often choose not to file charges at all.

“If you slap someone in the face, and they come back with a baseball bat,” however, “that’s no longer self-defense,” Goldman clarifies. If someone throws a punch and the other responds with a weapon, the weapon-wielder usually can’t claim self-defense.

If you are ever in the unfortunate circumstance of being charged with assault or battery, it’s important to know that there are gradations in the possible charges. Even once those charges are filed, an experienced criminal defense lawyer can often negotiate with prosecutors to obtain a reduction in the severity of the charges or to have them dismissed. No matter whether you’re charged with a felony or misdemeanor, you should seek the assistance of a defense attorney immediately.