The most runs, though only twenty at best (3,5)
I believe the answer is:
top score
'the most runs though only' is the definition.
I know nothing about this answer so I can't tell whether it can be defined by this definition.
'twenty at best' is the wordplay.
'twenty' becomes 'score' (synonyms).
'at' says to put letters next to each other (I've seen this in other clues).
'best' becomes 'top' (top can mean the very best).
'score' put after 'top' is 'TOP SCORE'.
Can you help me to learn more?
(Another definition for top score that I've seen is " one hundred and eighty!".)