When did Tang Xiaolong start to call knife elder brother?

After getting out of prison. Tang Xiaolong is one of the important figures in The Knockout. When he was serving his sentence, he often answered that it would be a crime to be called by his name after he was released from prison, so he simply called him knife elder brother to ease his embarrassment. The Knockout is an anti-gang criminal investigation drama jointly produced by CCTV, iQiyi, Bai Liu Film and Television and China Changan Publishing Media.