Read about challenge (4)
I believe the answer is:
dare
'challenge' is the definition.
(I know that dare is a type of challenge)
'read about' is the wordplay.
'about' indicates anagramming the letters.
'read' with letters rearranged gives 'DARE'.
(Other definitions for dare that I've seen before include "Challenge of courage" , "Take a chance - read about it" , "Have the courage to try something" , "Venture, have courage" , "Challenge to do something dangerous" .)