Battle of Un no Kuchi
The Battle of Un no Kuchi in 1536 was the first major victory for Takeda Harunobu, aged fifteen at the time. He would later take on the name Takeda Shingen, and grow to become one of Japan's most famous warlords.
Harunobu's father, Takeda Nobutora, attacked Hiraga Genshin in his fortress at Un no Kuchi, but was forced to retreat. Harunobu, at the rear of the withdrawing forces, waited until they were clear of the fortress, and then turned around, leading his men to defeat a castle garrison which was caught unprepared, having seen the Takeda flee.