The former assistant, Melissa Ishage, said in the complaint Williams became angry Tuesday and threatened to strike her, raising an open hand to her, The Hollywood Reporter said.
Williams then struck Ishage with a closed fist, causing serious injury, the documents said.
Ishage is seeking $5 million for assault, battery and intentional infliction of emotional distress, in addition to hospital and attorney fees.
Williams will appear in the upcoming "Scary Movie 5."
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