Top fielder, scratching head in confusion, to drop the ball (6)
I believe the answer is:
fumble
'drop the ball' is the definition.
'fumble' can be an answer for 'drop' (thesaurus). I'm not sure about the 'the ball' bit.
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for fumble that I've seen before include "Touch or handle clumsily, perhaps in pocket" , "Handle something awkwardly" , "Use the hands clumsily" , "Handle awkwardly, grope about" , "Grope around" .)