Make a score of 40 or 50 in encounter (5)
I believe the answer is:
halve
'make a score of 40 or' is the definition.
I can't judge whether this definition defines the answer.
'50 in encounter' is the wordplay.
'50' becomes 'l' (Roman numeral).
'in' means one lot of letters goes inside another.
'encounter' becomes 'have' (I can't justify this - if you can you should believe this answer much more).
'l' inserted within 'have' is 'HALVE'.
Can you help me to learn more?
(Other definitions for halve that I've seen before include "Reduce by a factor of two" , "Reduce by 50%" , "Cut into two equal portions" , "cut by fifty percent" , "Divide equally between two" .)