Quintessential Scots girl endlessly seen in cricket club (7)
I believe the answer is:
classic
'quintessential' is the definition.
(I've seen this before)
'scots girl endlessly seen in cricket club' is the wordplay.
'scots girl' becomes 'lassie' (I've seen this before).
'endlessly' means to remove the last letter.
'seen in' means one lot of letters goes inside another.
'cricket club' becomes 'cc'.
'lassie' with its last letter taken away is 'lassi'.
'lassi' put within 'cc' is 'CLASSIC'.
(Other definitions for classic that I've seen before include "Race, eg Derby" , "of enduring significance" , "The best of its kind" , "Serving as a standard - of the highest quality" , "Top-quality" .)