The word pitch, as it’s used here, means the highest point a bird reaches in flight.  Flavius compares Caesar to a bird of prey, like a hawk or a falcon, which soars up at a steep pitch before diving down to seize its quarry. And just as plucking a hawk’s feathers would keep it from soaring over its prey, Flavius hopes that removing the decorations from Caesar’s statues will prevent Caesar from flying too high above ordinary Roman citizens.