SPL: Kill Zone (2005) on Netflix

Plot summary

Hong Kong inspector Chan Kwok Chung has spent years chasing triad boss Wong Po. While Chan escorts a witness who holds evidence against Wong Po to court, another car rams them, and the assassin Jack kills the witness; Wong Po goes free. Chan survives, but doctors find a tumor in his brain. Three years later, Chan is nearing retirement and has adopted the slain witness's daughter, and his team, Wah, Sum and Lok, are protective of him. Ma Kwan arrives from another precinct to take over the unit. When a shop owner brings in a tape of Wong Po beating an undercover agent, Chan and his men see a way to frame him. Ma, who once beat a drug trafficker so badly the man was left mentally handicapped, has sworn off questionable methods.