Harry Brown (2009)
Harry Brown is a 2009 British vigilante film directed by Daniel Barber and starring Michael Caine, Emily Mortimer, Jack O'Connell, and Liam Cunningham. The story follows Harry Brown, a widowed Royal Marines veteran, who had served in Northern Ireland during The Troubles, living on a London housing estate that is rapidly descending into youth crime; Harry fights fire with fire after a friend is murdered.
More at Wikipedia.