Stop to drink beer, mostly that's extremely common (9)
I believe the answer is:
prevalent
'extremely common' is the definition.
'prevalent' can be an answer for 'common' (prevalent can mean common or widespread). I'm not certain of the 'extremely' bit.
'stop to drink beer mostly' is the wordplay.
'stop' becomes 'prevent' (I've seen this before).
'to drink' means one lot of letters goes inside another.
'beer' becomes 'ale' (type of beer).
'mostly' means to remove the last letter.
'ale' with its last letter removed is 'al'.
'prevent' placed around 'al' is 'PREVALENT'.
'that's' acts as a link.
Can you help me to learn more?
(Other definitions for prevalent that I've seen before include "Widely accepted" , "general" , "Common" , "Commonplace" , "Ruling" .)