From a communication perspective, any nonverbal cue is ambiguous if it is demonstrated singly without a clear verbal expression. For example, the nonverbal behavior of raising a hand could be intepreted in multiple ways. It could be interpreted as "protecting your fetus (baby)", or "protecting yourself" or "pushing her away when you perceived that there was an immediate danger for your well being."
So my point is: A nonberbal behavior does not have a specitific meaning until you verbally define it. At this point, nobody could specifically say for sure that "your gesture is indicating that you are going to slap her in the face." Therefore, the video of a hand movement "without a clear verbal expression" can not be a strong evidence of an assaulting behavior.
