A leather jacket or a heavy punching bag provides a perfect mid-range "slap."
Sound effects provide subtle clues about a character's physical state or the severity of an injury without needing dialogue. 4. Where to Find Professional SFX body_impacts_sound_effect
You don't always need a recording of a real "fight" to get a great impact. Sound designers often use creative Foley techniques to build these layers: A leather jacket or a heavy punching bag