Master Gautama was born a prince, but he renounced his comfortable life and became a beggar in the forests of Nepal. Giving up position in his own caste, he openly taught his wisdom to anyone of any caste and even women and gave simple examples based upon the ability of the listener to understand.
Gautama's dharma was intended as a self help aid to end psychological suffering.
But when Buddhism was brought to China and later to Japan and Korea, the emperor didn't want a large population of beggars, perhaps 10% of the population, seeking enlightenment instead of working and paying taxes.
So Buddhism was institutionalized in the three countries. There was great competition for political recognition, the title of "national teacher" and imperial funding and the Ch'an/Zen/Seon monasteries became places where a monk could spend a lifetime as a laborer, never progressing, or he could compete with the other monks, hoping for tenure or to establish his own temple where he could pretend to "teach" novice monks.
The Zen koan was invented as a way to screen out the truly stupid novice and provide a clue to bring the most intelligent novice to enlightenment, before leaving the monastery and returning to private life or starting his own temple.
The "sound of one hand" koan refers to the beating of the human heart.
Ancients didn't know for sure where the mind was located and they thought that the mind and heart were probably in the same place.
Ancient yoga instructions tell the meditator to regulate his breathing, stop thinking, and slow his heartbeat down in order to become One with the Self (aka Brahman).
That's all there is to it, no "dharma combat" is necessary, unless the modern Zen master is trying to keep the modern novice from becoming enlightened.
Why do that, unless the intent of the Zen master is to
milk the novice for all the money he can get?