The Battle of Sphacteria in 425 B.C. was part of the Second Peloponnesian War between the Greek city states of Athens and Sparta and was pretty much a foregone conclusion after the Athenians won the Battle of Pylos and isolated the Spartan forces without supply. Cleon brought reinforcement for Demosthenes and the two generals overwhelmed the Spartans taking 292 prisoners. It was almost unheard of for Spartans to surrender, and the Spartans sued for peace. Cleon, in a move that can be judged more clearly in retrospect, foolishly refused.
Sources
Encyclopedia of Military History, Dupuy & Dupuy, 1979