Twenty runs — I'll record that (6)
I believe the answer is:
scorer
'twenty runs i'll record that' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'twenty runs' is the wordplay.
'twenty' becomes 'score' (synonyms).
'runs' becomes 'r' (cricket abbreviation).
'score'+'r'='SCORER'
(Other definitions for scorer that I've seen before include "Cricket official" , "One getting a goal" , "He scratches" , "who makes a point?" , "He puts the ball in the net" .)