Transcript for Dramatic video shows Russian opposition leader Alexei Navalny arrested by police

Overseas tonight, we turn to Russia, and outrage over the arrest of Putin's biggest political rival. Taken into custody during a protest. Barred from running for president, calling for a boycott of the election. Our cameras showing how Putin's forces crack down on protesters. Here's Dan Harris. Reporter: In dramatic video tonight, you can see opposition leader alexei navalny arrested on the streets of Moscow while taking part in an anti-putin rally. Hours earlier, police raided his group's offices, interrupting a newscast and arresting one of the anchors. Alexei navalny has been called "The man Vladimir Putin fears most." He's been banned from running in the upcoming presidential election, after having spent years leading anti-kremlin rallies during which he has been publicly beaten and even once nearly blinded when someone sprayed green liquid in his face. We saw firsthand in October how police in Russia handle protesters. Wading into the crowd, and apparently even sending in provocateurs. Is he trying to start a fight? Yes. Reporter: This kind of thing in America, nobody bats an eye. People protest the government all the time. Here, it's a radical act. Tonight, navalni, just released, is calling for a boycott of the March 18th presidential election. But with Vladimir Putin's popularity rate hovering around 80%, the outcome is all but certain. Dan Harris, ABC news, New York.

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