Another favorite:

The Spartans were composed of two morai led by the polemarchoi Gorgoleon and Theopompus.[38][note 3] They outnumbered the Thebans at least two to one.[37] According to Plutarch, upon seeing the Spartans, one Theban allegedly told Pelopidas “We are fallen into our enemy’s hands” to which Pelopidas replied, “And why not they into ours?” He then ordered his cavalry to ride up from the rear and charge while he reformed the Sacred Band into an abnormally dense formation, hoping to at least cut through the numerically superior Spartan lines. The Spartans advanced, confident in their numbers, only to have their leaders killed immediately in the opening clashes. Leaderless and encountering forces equal in discipline and training for the first time in the Sacred Band, the Spartans faltered and opened their ranks, expecting the Thebans to pass through and escape. Instead, Pelopidas surprised them by using the opening to flank the Spartans.[39] The Spartans were completely routed, with considerable loss of life.[20][40] The Thebans didn’t pursue the fleeing survivors, mindful of the remaining Spartan mora stationed in Orchomenus less than 5 km (3.1 mi) away. They stripped the dead and set up a tropaion (τρόπαιον, a commemorative trophy left at the site of a battle victory) before continuing on to Thebes.[19] Having proven their worth, Pelopidas kept the Sacred Band as a separate tactical unit in all subsequent battles.[6][20]