The man was whacked with the bird while he filmed the annual "duck chase" in the Catalonian seaside town of Roses, where every August ducks are thrown into the Mediterranean and then caught and brought back to the shore by swimmers.
"Continue, continue. Continue to abuse, I am filming you. A little bit of empathy for the animals. They also have a life, like your children or your family," the man who was filming can be heard saying in a video of the incident released by animal rights group Animal Rescue España.
The footage shows a young woman wearing a white bathing suit attack the man with a duck -- holding it by the legs as she repeatedly lashes him with it.
As the attack goes on, animal rights activists gathered on the shore can be heard chanting, "You would not do that to your dog," before they were removed by police.
Every year since 1918 about 50 ducks are thrown into the sea in the town north of Barcelona, with swimmers then racing in to catch them and bringing them ashore however they can.
But after Sunday's incident, the town's mayor is mulling putting an end to the "duck chase".
Interviewed by local online news site Emporda, the mayor of Roses, Montse Mindan, prosposed "holding a referendum next year on what residents think, if they want to keep this festival, a tradition that will celebrate its centenary in two years."
'Pain, fear and suffering'
While the ducks are not killed, Animal Rescue Espana said they suffer "stress, internal hemorrhaging, pain, fear and suffering."
The group launched a petition on the Change.org website demanding that Roses ban the "duck chase" as well as bull runs.
The petition has received over 10,000 signatures since it was launched on August 14.
Spain has many controversial animal-based traditions, often in honour of patron saints, which animal rights groups argue are cruel.
Bull runs, where people run ahead of a pack of half-tonne fighting bulls, are a part of summer festivals across the country, the most famous during the San Fermin feria in Pamplona.
At least nine people have lost their lives at bull festivals since the beginning of June, including one man who was gored in the neck earlier this month while filming a run on his mobile phone.
Festivities at the annual San Antolin festival in the Basque coastal town of Lekeitio revolve around a contest where young men battle to pull the head off a dead goose as it is dragged on a pulley across the harbour.
Previously a live goose was used.
Villagers in the northern village of Manganeses de la Polvorosa used to hurl a live goat from the top of their church tower to honour its patron saint but the practice was banned in 1992.