The most commonly used name by City fans to describe their cross-city rivals is the term "The Rags", this is due to a period after World War II where United were given use of City's Maine Road stadium after Old Trafford had been bombed by the Luftwaffe.Care to elaborate here please.
War banter it seems.
Or maybe not.
How United became the 'Rags'
by Gary James’ from "Manchester - The Greatest City".
It appears the name was given to them by their own fans.
During the 1930-31 season, United were in a wretched state. The club teetered on the brink of bankruptcy and were attracting crowds of less than 4,000 for some games - despite still being in Division 1.
Harry Hughes, a City fan working in Trafford, tells this story:
“I worked in Trafford then, and all the locals were United fans. I was working nights and when Saturday morning arrived a couple of them asked ‘are you going to see the Rags today?’ I didn’t know what that meant, and then they explained that United fans had started to call their own team the ‘Rags’ because they were so poor and that their kit looked liked rags. So after that I knew who they meant, but when I mentioned the Rags, they’d go, ‘who the Hell are you talking about?’ They didn’t like the opposition saying it.”
The poor level of support continued throughout the 1930s. When war broke out in 1939 an immediate ban was placed on the assembly of large crowds. The joke doing the rounds in Manchester was that United would have nothing to worry about.