Apparent big scores by one British left half (10)
I believe the answer is:
ostensible
'apparent' is the definition.
(synonyms)
'big scores by one british left half' is the wordplay.
I cannot quite understand how this works, but
'big' could be 'os' and 'os' is found within the answer.
'one' could be 'i' (Roman numeral) and 'i' is located in the answer.
'british' could be 'b' (abbreviation e.g. in 'BBC') and 'b' is found in the answer.
'left' could be 'l' (common abbreviation) and 'l' is located in the answer.
The remaining letters 'tense' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for ostensible that I've seen before include "Apparent" , "Apparently true" , "Professed" , "Manifest" , "Supposed" .)