Someone who is fighting mad, perhaps a crazed fighter who has no thought for his own health and well being.
Dogs engaged in attack can indeed exhibit this kind of no-holds-barred viciousness, so perhaps it is apt. George Orwell classes this term, along with others “peculiar to Marxist writing.” He included “lackey” and “petty bourgeois” in this category. I guess that they hadn't started using “running dog” yet. That came later. Perhaps it was just that Orwell didn't much like Noel Coward, whose 1931 song, “Mad dogs and Englishmen” noted that Anglo cultures are anomalous for going out in the midday sun, while any sensible society takes a siesta in the shade. Once again, the image is of someone who is thoughtless of personal safety and without sense.
I also came across this wonderful discussion of metaphor, using mad dog as the example:
| We are arguing in this work that metaphors are statements which symbols refer to the entity called image-state. And the propositional form of a metaphor ('A is B') is a key element in their understanding. This form requires that A could be seen as B, or that dynamics of A is the same as dynamics of B. The only difference between metaphorical statement John is a mad dog and the statement John is a man is in the way we used to analyze them. In the case of a literal statement ('John is a man') we will search for absolute match between properties of two arguments of the statement. In the case of metaphorical statement ('John is a mad dog') John would be seen as a mad dog.
1. Orwell, George. 1946. Politics and the English Language. In In Front of Your Nose, 1945-1950, edited by I. S. O. Angus. Boston: David R Godine.
2. Knowles, Elizabeth. 1999. The Oxford Dictionary of Quotations. 5th ed. Oxford; New York: Oxford University Press.
3. Repeko, Alexander. 1999. Understanding Metaphorical Statements, Cognitive Science Department, New Bulgarian University.