In modern English, sycophancy primarily refers to obsequious flattery, but in Cleon‘s time it meant something quite different:
The death of Pericles from the plague in 429 BC left the field clear for new leadership in Athens. Hitherto Cleon had only been a vigorous opposition speaker, a trenchant critic and accuser of state officials, but he now came forward as the professed champion and leader of the democracy and, as a result, dominated Athenian politics. Although rough and unpolished, he was charismatic, being gifted with natural eloquence and a powerful voice, and he knew how to work upon the emotions of the Athenian populace. He strengthened his support amongst the poorer citizens of Athens by increasing the pay of the jurymen, which provided many of the poorer Athenians with a means of livelihood.The fondness of the Athenians for litigation increased his power; and the practice of “sycophancy” (raking up material for false charges), enabled him to remove those who were likely to endanger his ascendancy.