A much longer explanation than the joke itself (which is probably a mercy) - In English law there is the offence of common assault, which comprises two parts - assault and battery. Taking the example of someone taking a swing at someone else, the assault is complete when the victim fears imminent injury, whether the blow makes contact or not. The battery part is complete when the blow connects.
I once arrested a man for battery - the Sergeant told me to put him in a dry cell and charge him in the morning.
