According to new legal docs, obtained by TMZ, a woman who says she was working on the riverboat told police one of the white men who attacked a Black deckhand yelled, "F*** that n*****" before coming down the dock to fight him.

The woman, Crystal Warren, claims the alleged n-bomb dropped after the Black deckhand moved a couple of smaller boats that were taking up space on the dock and preventing the riverboat from docking.

Warren told police the riverboat captain initially asked the boat owners to move their boat, which she said drew middle fingers and curses from the white men on the boat. She says the riverboat was stuck waiting for 17 minutes until a smaller commercial boat picked up a deckhand and her 16-year-old son from the riverboat and dropped them off on the dock.

From there, Warren claims the deckhand and her son Daniel moved the boats that were blocking the dock and tied them back up, and she says she heard at least one of the men yell the n-word.

Warren also claims one of the white men threatened to go and get a gun during the fight on the dock ... a brawl that was captured on video and has already led to at least one arrest.

The viral video appears to show Daniel trying to pull the white men off the Black deckhand, and his mother says he was punched in the chest while trying to break up the fight, suffering bruised ribs and going to a hospital for a diagnosis.

Richard Roberts is the man accused of punching Daniel ... and he's been arrested and charged with 3rd-degree assault