Fielder’s success, perhaps, an unexpected difficulty (5)
I believe the answer is:
catch
'unexpected difficulty' is the definition.
I don't understand how the remainder of the clue works.
(Other definitions for catch that I've seen before include "Book by Joseph Heller" , "Apprehend - funny song" , "Ensnare" , "fellow hooked for matrimony?" , "Get a grip on" .)