>>546405015
The traditional narrative is that it was this huge, badass battle between two armies, East and West. The armies both looked at each other for hours until general Fukushima of the East started the engagement at Sekigahara. Ieyasu, commander of the Eastern forces, was outnumbered, but he had convinced several generals of the West to remain in their positions without engaging (Mouri and Chousokabe). However, Ieyasu was still waiting to see Kobayakawa Hideaki's actions, see what he would do. Kobayakawa was being indecisive and his support was crucial. In a moment of impatience, Ieyasu decided to stop waiting for Kobayakawa to answer and started shooting Kobayakawa's troops. This prompted Kobayakawa to act and finally pledge his support for Ieyasu. Despite the West's superior numbers, Kobayakawa's defection was a crippling blow. The Western strategy, Outani Yoshitsugu, valiantly fought Kobayakawa's large regiment, but was ultimately killed. The generals of the West fought bravely, but were captured or killed. Despite this loss, the West still fought honorably.
Kobayakawa was seen as a piece of shit for his dishonorable betrayal and was shunned by all.

The sources though show that Kobayakawa was willing to defect from the start and his regiment moved to the high ground first. Outani thought it was suspicious, so he followed Kobayakawa. Once these two forces engaged, the rest of the East followed and the West was swiftly defeated in a couple of hours. Kobayakawa was rewarded for his service.