RIA Novosti said the protest took place in the city of Voronezh.
Activists had announced earlier they would picket there, RIA Novosti said, and several hundred opponents gathered there to stop the protest.
RIA Novosti said the opponents sealed off all the entrances to the area to prevent the rally.
When the first 10 activists appeared, the crowd pelted them with snowballs and then beat them, RIA Novosti reported.
Police said at least one picketer had to seek medical assistance.
RIA Novosti said homosexuality was decriminalized in Russia in 1993 but attitudes toward gays and lesbians remain hostile.
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