Second mate overlooking one part of rigging (4)
I believe the answer is:
spar
'part of rigging' is the definition.
(I've seen this before)
'second mate overlooking one' is the wordplay.
'second' becomes 's' (common abbreviation).
'mate' becomes 'pr' (I can't explain this - if you can you should give a lot more credence to this answer).
'overlooking' indicates putting letters inside (in a down clue, some letters go above others).
'one' becomes 'a' (a thing is one thing).
'pr' placed around 'a' is 'par'.
's'+'par'='SPAR'
Can you help me to learn more?
(Other definitions for spar that I've seen before include "Box; various minerals" , "Practise boxing with a pole?" , "Sticks" , "Do up (bird for oven)" , "Mast - boom - gaff" .)