Until Friday, at least, the cable news coverage of the first criminal trial of a former president carried a hint of anticlimax.

With the dry and slow-moving proceedings inside a Lower Manhattan courtroom closed to their cameras, the networks could only offer their usual interviews with experts and analysts, set to the sights and sounds of their outdoor, on-location camera positions.

That all changed on Friday when a man from Florida, Max Azzarello, set himself on fire near the courthouse — immediately bringing home the promise and perils of live cable news, especially for the network that invented the genre, CNN.

The network’s legal analyst and anchor, Laura Coates, was doing a live interview with a jury-selection expert when Mr. Azzarello began throwing a batch of conspiracy pamphlets into the air, then dousing himself with an accelerant and setting himself ablaze.

Ms. Coates broke away from a conversation about sequestration rules to dramatically convey what was unfolding nearby.

“An active shooter, an active shooter is in the park outside the court,’’ she shouted excitedly, and incorrectly, before quickly realizing what she was witnessing: “We have a man, he has set fire to himself, a man has emblazoned himself outside of the courthouse just now. Our cameras are turning right now.”