End of leg struck incomplete unit (6)
I believe the answer is:
gramme
'unit' is the definition.
(gramme is a kind of unit)
'end of leg struck incomplete' is the wordplay.
'end of leg' becomes 'g' (I can't explain this - if you can you should give a lot more credence to this answer).
'struck' becomes 'rammed' (I've seen this in another clue).
'incomplete' means to remove the last letter.
'rammed' with its final letter taken away is 'ramme'.
'g'+'ramme'='GRAMME'
Can you help me to learn more?
(Other definitions for gramme that I've seen before include "Metric unit of weight" , "Small weight" , "One thousandth of a kilogram (Fr)" , "Arm Meg (anag)" , "Small unit of mass" .)