Dragon (2011) on Netflix

Plot summary

The year is 1917, and Liu Jin-Xi makes his living as a papermaker in a village in Yunnan, sharing a house with his wife, Yu, and two sons, Fangzheng and Xiaotian. Two robbers come into a shop where he is and attempt a robbery, and a brawl follows in which Liu kills both of them. The villagers celebrate him as a hero. Xu Bai-Jiu, the detective assigned to the case, examines the bodies and finds that one robber, a fighter of great skill, died when a blow to the vagus nerve caused bleeding in his brain. Xu questions how Liu could have killed such a man by accident.