The Boxer is dark movie about a seemingly unsolvable problem. It's filmed in a constant dark, dreary, depressing light; this light reflects not only the weather but the mood of Northern Ireland.
This expose of "the troubles" in N. Ireland uses a story about a boxer who returns to his home after being released after 14 years of imprisonment. His goal is to take his most usable asset (boxing) and make something of himself and his former coach.
Like everything in N. Ireland, living normally is laced with problems when you're in the middle of a war. His interest in his now-married former girlfriend is forbidden, since prisoners of war wives are off limits to honor the prisoner. Accepting gifts from the police force is also a sign of capitulation, and as such carries penalties.
The film clearly shows that those that wish to make peace (however passively) and live normal lives are marked as disloyal and targeted by the Irish Mafia (alluded to as the IRA in the film).
It's a sad commentary on a desolate group of trouble makers in a growing desolate land.