Be greatly entertained to be ready for soccer? (4,1,4)
I believe the answer is:
have a ball
'be greatly entertained' is the definition.
(to have a ball is to be entertained or amused)
I don't understand how the remainder of the clue works.
(Other definitions for have a ball that I've seen before include "Let your hair down" , "Enjoy oneself very much" , "Ref coming on to pitch will" , "as debutantes did?" , "Enjoy oneself greatly" .)