World chess body admits limits of diagonal play (6)
I believe the answer is:
fiddle
'play' is the definition.
(fiddling is a kind of playing)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for fiddle that I've seen before include "Get by cheating, or handle aimlessly" , "Fix" , "Violin - racket" , "One's played" , "Commit fraud; instrument" .)