I'm scouring the Internet right now, but I can't begin to find a news article about the bludgeoning incident DMan described in his (now deleted) writeup. Anyways --
"Black rage" is a phrase which summarizes all the anger, frustration, and sometimes outright hatred which many black Americans experience in response to the subtle racism of American society. It was coined by psychiatrists Price Cobbs and William Grier in their 1968 book of the same name.
When employed as a legal defense, it argues that formative events in the defendant's past, events which were directly or indirectly caused by their racial profile, led to their emotional state when the crime was committed. The first such use of this defense dates to 1946, when William Henry Seward argued that the consequences of black slavery and the ongoing oppression of blacks in the United States drove William Freeman to madness and murder.
The "black rage defense", however, is not a freestanding legal defense which demands the acquital of the black person on trial. It is simply a race-specific term for the long-standing state of mind or environmental defense, or even temporary insanity, arguing that an individual's mindset or expectations of danger should affect how severely their crime is judged. It's identical to defenses used in other cases for battered women or ex-soldiers suffering post-traumatic stress syndrome.
Because racism is now a four-letter word in American society, the concept of a "black rage defense" is anathema to many people. It sounds like a courtroom version of affirmative action, but it's not. The latter is an attempt to reverse discrimination through reverse discrimination, regardless of the individual, while the former is an attempt to explain the actions of one individual on trial for one crime. And like any legal argument, it falls to the judge and jury to determine its validity.
Recommended reading: "Black Rage Confronts the Law"
by Paul Harris