Hyakujo wanted to choose an abbot for the Daii Monastery. He told the head monk and all the rest of his disciples to make their Zen presentations, and the ablest one would be sent to found the monastery.
Then Hyakujo took a pitcher, placed it on the floor, and asked the question: "This must not be called a pitcher. What do you call it?" The head monk said, "It cannot be called a wooden sandal." Hyakujo then asked Isan. Isan walked up, kicked over the pitcher, and left.
Hyakujo said, "The head monk has been defeated by Isan." So Isan was ordered to start the monastery.--- From The Gateless Barrier:
Zen Comments on the Mumonkan