"A whole riot of people came running down the block," said FoFo Beniquez, 19, who saw the fighting shortly after 9 p.m. Sunday on South Fourth Street, in Williamsburg.
"They were fighting, throwing punches in the middle of the street."
A 21-year-old man was slashed on his right arm, police said A 28-year-old man was hit in the head "with a blunt object" in the fights between Keap and Hooper streets shortly after 9 p.m., police said.
The 21-year-old "was screaming and looked mad," Beniquez said. "You could see the blood running down the back of his shirt. People were trying to back him away from the crowd.''
The other casualty might have been hit with a bottle, a police source said.
Both men were taken to Bellevue Hospital in stable condition, police said.
Neither victim has been identified.
Nine people, including four teenagers, were arrested: Tatiana Cabrera, 17, and Jackelyn Garcia, 35, were charged with unlawful assembly; Ernesto Carabello, 21, Michael Hernandez, 26, and Edwin Fermin, 22, were charged with disorderly conduct; Yaritsa Gomez, 28, and Ashley Vinas, 18, were charged with resisting arrest and disorderly conduct; Danny Cabrera, 36, was charged with obstruction of governmental administration, unlawful assembly and disorderly conduct; and an unidentified 15-year-old boy was charged with criminal possession of marijuana.
They were awaiting arraignment Monday at Brooklyn Criminal Court.
Hours before the block party, about a half million revelers lined Sixth Avenue in Manhattan for the 30th annual Dominican Day Parade.