Fielder, Mike I assume (3-2)
I believe the answer is:
mid-on
'fielder' is the definition.
(I've seen this before)
'mike i assume' is the wordplay.
'mike' becomes 'M' (phonetic alphabet: alpha, bravo, charlie etc.).
'assume' becomes 'don' (I've seen this in another clue).
'm'+'i'+'don'='MID-ON'
(Other definitions for mid-on that I've seen before include "Cricket fielder" , "Leg side fieldsman" , "Fielding position" , "Cricketing position" .)