11. Won a slam on hard court, clay and grass all in the same season(9,4)
20. When His friend was kidnapped he wanted to send a message to the FBI for Help (3,3,5,8)
48. Two of his paintings were acquired By the New York's Museum Of Art and The British Museum of Modern art By the time he was 20. (4,4)
51. Homer Simpson's Personal Hero(5,7)
Steffi (Stefanie) Graf with possible incorrect spelling of her first name?
Graf (male) or Gräfin (female) is a historical title of the German nobility, usually translated as "count". Considered to be intermediate among noble ranks, the title is often treated as equivalent to the British title of "earl" (whose female version is "countess")
//All answers are people/animals, real or imaginary, who have a title or Royal rank somewhere in their name. Not all titles/ranks are from the U.K. They can come from anywhere in the world//
For 48 Naum Gabo is 4,4, although he was more well known as a sculptor rather than for his paintings. I can't see the class link either. Will keep thinking