Over 50 invading large Eastern force (6)
I believe the answer is:
oblige
'force' is the definition.
(I've seen this in another clue)
'over 50 invading large eastern' is the wordplay.
I cannot quite understand how this works, but
'over' could be 'o' (cricket abbreviation) and 'o' is located in the answer.
'50' could be 'l' (Roman numeral) and 'l' is located in the answer.
'large' could be 'big' (synonyms) and 'big' is found in the leftover letters.
'eastern' could be 'e' and 'e' is located in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for oblige that I've seen before include "Compel (someone to do something)" , "Compel, bind" , "serve" , "Morally influence" , "Constrain" .)