Assault and battery is a very common crime. The two words go hand in hand, but in actual fact, they are two separate crimes.
As an officer, you will need to distinguish between the two when investigating a call.
An assault takes place when anyone threatens to use force against another person. If one person clenches his fist, cocks his hand backward as if to throw a punch at the other person, he has committed an assault. No strike has actually been thrown at this point in this example, but it doesn't matter. In other words, if you intend to threaten, intimidate or scare someone with that gesture, and that person believes that you are capable and intend to do so, its an assault.
Perhaps you don't actually strike the other person, but you've still committed the crime.
The battery takes place when the suspect follows through and actually throws the punch, striking the victim. In other words, there is actual contact between the suspect and the victim. Obviously, in this example, the suspect throws a punch.
But The contact can be indirect contact between the suspect against the victim. Opening a car door quickly and purposely striking someone, or throwing a ball and hitting someone is also battery. (Obviously only if you intend to hit and hurt someone. Playing softball and trying to throw at the runner at second and the ball accidentally hitting them is not a crime.)
So, you can see that an assault can actually take place on it's own. No actual contact, then there's no battery.
On the other hand, when someone is arrested for battery, the charge of assault is included in the arrest because by definition a battery cannot take place without it.