Over 50 in substantial English force (6)
I believe the answer is:
oblige
'force' is the definition.
(I know that force is a more specific form of oblige)
'over 50 in substantial english' 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 found in the answer.
'substantial' could be 'big' (I've seen this in another clue) and 'big' is found within the leftover letters.
'english' could be 'e' (abbreviation) and 'e' is found within the answer.
No letters remain.
This explanation may well be incorrect...
(Other definitions for oblige that I've seen before include "Coerce or accommodate" , "Hold in debt" , "Bind morally or legally" , "Compel (someone to do something)" , "Constrain" .)