A cricket club almost entirely adopting rugby as additional item (7)
I believe the answer is:
accrual
'additional item' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'a cricket club almost entirely adopting rugby' is the wordplay.
'cricket club' becomes 'cc' (cricketing abbreviation).
'almost' means to remove the last letter (most of the word but not all of it).
'entirely' becomes 'all' (all can mean entirely or completely).
'adopting' means one lot of letters goes inside another (inserted letters are taken on or adopted).
'rugby' becomes 'RU'.
'all' with its final letter taken off is 'al'.
'cc'+'al'='ccal'
'ccal' placed around 'ru' is 'ccrual'.
'a'+'ccrual'='ACCRUAL'
'as' is the link.
Can you help me to learn more?
(Other definitions for accrual that I've seen before include "Something building up" , "A charge to be paid in a future acounting period" , "Build up of regularly received amounts" , "Slow increase (of e.g. capital)" , "A building up (of money)" .)