Protests tend to be more prominent on news broadcasts.
There was a protest that delayed the opening to the "CBS Evening News with Dan Rather" in the early 1990s. TVParty has a clip of it.
If you wanna go full blown reversal, Rather staged protest on US Open tennis coverage in 1987. He left the studio and CBS was literally stuck with dead air.
On a local level in the Philadelphia market, Larry Kane, the dean of Philadelphia newscasters, wrote of a most interesting protest that occurred during his time with WPVI-TV's Action News in the 1970s in his book "Larry Kane's Philadelphia". I'll have to dig around and find the excerpt, but I believe it involved Channel 6's late great weatherman Jim O' Brien having to beat the crap out of one of the protesters against the old magnetic weather map.
Edit: Found said protest. Here's the small of it. A group called The Gay Raiders interrupted midway through a July 1972 Action News broadcast. Kane recalls that he was reading a story about youth violence and then he heard someone say to him, "Mr. Kane, we demand justice." From there, a grabbing struggle occurred on camera briefly. The director goes to black and to quote Kane from a paragraph in the book:
"Then the real fun began. Jim O'Brien, our weatherman, went into hand-to-hand combat with the protest leader. Sportscaster Joe Pellegrino ran after the other three invaders and pinned one of them against the wall. When the news returned to the airwaves, O'Brien was near the point of severely beating my visitor. Along with the highs and lows, blood appeared on the weather wall, near the state of Illinois. The viewing audience never saw the violence, but it was a heavyweight struggle." (Found on Page 76 of Larry Kane's Philadelphia, published by Temple University Press).
