Fielder I'm about to send off (3-3)
I believe the answer is:
mid-off
'fielder' is the definition.
(I've seen this before)
'i'm about to send off' is the wordplay.
'about' says the letters should be written backwards.
'to send off' becomes 'doff' (I am not sure about this - if you are sure you should believe this answer much more).
'im' in reverse letter order is 'mi'.
'mi'+'doff'='MID-OFF'
Can you help me to learn more?
(Other definitions for mid-off that I've seen before include "Cricket fielding position" , "Position in the field" , "Someone in field" .)