The battle of Olynthus (382 BC) was a near defeat for a Spartan army that had been sent north to more vigorously conduct the war against Olynthus that had begun earlier in the same year.
In the years before 382 Olynthus had put itself at the head of a Chalcidian League, which had also expanded at the expense of Amyntas III of Macdeon. Early in the year both Amyntas and the Chalcidian cities of Acanthus and Apollonia had sent envoys to Sparta asking for assistance, and the Spartans had responded by sending an army north. This first army moved in two waves. An advance guard under Eudamidas actually reached Chalcidice, and where it some successes before getting bogged down. The larger second wave only got as far at Thebes, where the commander Phoebidas became involved in local politics, seized the Cadmea (the acropolis of Thebes), and took control of the city.
Later in the year the Spartans decided to send fresh troops to conduct the war against Olynthus, this time commanded by Teleutias, a half-brother of King Agesilaus II. According to Xenophon Teleutias was given 10,000 men, and also summoned troops from Sparta's allies has he headed north, Thebes, which had refused to support the original expedition, supplied troops. Amyntas of Macedon was urged to supply mercenaries. Teleutias also sent messengers to the Thracian king Derdas of Elimia, pointing out that he was also threatened by the rising power of Olynthus. Derdas joined the army with 400 cavalry. By the time Teleutias was close to Olynthus his army included Spartan, Peloponnesian, Theban and Macedonian contingents as well as the original army under Eudamidas.
After a brief pause at Potidaea, Teleutias advanced towards Olynthus. About a mile from the city he formed his army into a line of battle, with his own contingent, and Derdas's cavalry on the left, facing the city gate, and the allies, along with the Spartan, Theban and Macedonian cavalry, on the right.
The Olynthians responded to the challenge. They emerged from the city, formed up close to the walls, and then launched a cavalry attack on the Spartan right. The Spartan and Boeotian cavalry on the Spartan right was defeated, and the Spartan cavalry command Polycharmus killed. The allied infantry on the Spartan right was close to breaking.
Derdas saved the day, leading his cavalry in a charge against the city gates of Olynthus. Teleutias followed up with his infantry. This attack threatened to cut off the Olynthian cavalry, and it abandoned the attack and fled back to the city. Derdas was able to inflict heavy losses on the retreating Olynthians. The Olynthian infantry, which was still close to the city walls and doesn't appear to have been involved in the battle, was able to retreat back into the city without problems.
Although Teleutias claimed that the battle had been a victory, and even erected a victory trophy, he then withdrew from the immediate vicinity of the city. Derdas and the Macedonians were sent home. Over the winter the Olynthians appear to have held the initiative, raiding the territory of cities that had chosen to support the Spartans. Early in the following year a raid on Apollonia ended in defeat at the hands of Derdas, but the Olynthians had another success soon afterwards, defeating the Spartans and killing Teleutias (battle of Olynthus, 381 BC).
Xenophon, who provides the detailed account of this battle, doesn't provide any casualty figures. Diodorus only mentions a second battle in the following year, in which Teleutias was killed.