London Boulevard
(2010)

After Billy dies, and Gant (Ray Winstone) kills Mitchel's sister, Briony (Anna Friel) along with Dr. Sanji Raju and Mitchell (Colin Farrell), break into the bigoted crime boss' home and shoot him in the head.

Soon after, Mitchell is stabbed by one of the teenage punks (who earlier on, he tried to kill but couldn't.)

Thanks ND Woods!