A rabble-rousing politician deliberately gets their audience worked up into an angry frenzy. Sometimes a rabble-rousing speech even inspires listeners to violence.
A skilled public speaker can powerfully capture people's attention and inspire them to take action, get involved, or vote a certain way. A rabble-rousing speaker does nearly the same thing, but their goal is to get a crowd aggressively angry. They do this by manipulating the audience's prejudices and fears. Rabble-rousing, which dates back to the early 19th century, is from rabble, "pack of animals," and rouse, "to stir up or awaken."