What exactly is classed as an "assault" ?

Assault legally is the threat of force. Battery is the actual use of force.

And neither has to leave a mark, but it is nearly impossible to prove either if there are no marks and no witnesses.

I remember learning in law class that even telling someone that you are going to hurt them is considered an assault. The only exception is if you obviously are not physically able to carry out your threat – like being in a wheelchair on oxygen or something, or a 90-pound woman telling a 350 pound 7 foot guy that she is going to kick his a**.

@WestRiverrat So, accusing someone of assault, you need to have some kinda proof? Can the authorities take any action without there being any witnesses/marks?

“An assault is carried out by a threat of bodily harm coupled with an apparent, present ability to cause the harm. It is both a crime and a tort and, therefore, may result in either criminal or civil liability. Generally, the common law definition is the same in criminal and Tort Law. There is, however, an additional Criminal Law category of assault consisting of an attempted but unsuccessful Battery.

Statutory definitions of assault in the various jurisdictions throughout the United States are not substantially different from the common-law definition.”

Free legal Dictionary

That is a good question, @MilkyWay . How would you prove it – unless you had witnesses or surveillance footage or something.

@MilkyWay you can accuse all you want, but if you cannot convince a judge and/or jury that you had a valid reason to believe an assault did occur, you may end up on the wrong side of a malicious prosecution or defamation of character charge.

Okay, thank you everyone. Much appreciated :)

In the law an assault is putting someone in fear of immediate harm. People incorrectly use the term assault to mean an actual touching. The actual unwanted or harmful touch is a battery.