The scuffle broke out at the end of the opening ceremony of the four-day festival in front of the Academy of Fine Arts in downtown Sarajevo.
"When I was getting out of the academy, I was suddenly struck in the back," Pedja Kojovic, a local journalist, told AFP. "Three other people then came running and beat me up."
Emir Imamovic, a journalist who tried to help Kojovic, was severely beaten, police said. Another journalist was also injured.
A heavy police deployment prevented more violence from spoiling the event, with a security cordon keeping protestors shouting "kill the gays" and "Allahu Akbar" (a Muslim expression meaning God is Great) at bay.
A police officer on the scene said groups of anti-gay protestors had spread to nearby streets and were attacking people. A police officer was struck in the head during the clashes.
About 50 people participated in the opening day of the festival, which had already prompted fears of violence, with homophobia overriding usual divisions among the country's wartime foes -- Muslims, Serbs and Croats.
The country's Muslim majority is particularly upset about the festival because it opened during the Muslim holy month of Ramadan.
Many, including members of various ethnic political parties, have declared homosexuality an illness and labelled the behaviour deviant.