Somehow rents beers out in watchfulness (9)
I believe the answer is:
alertness
'watchfulness' is the definition.
(synonyms)
'somehow rents beers out' is the wordplay.
'somehow' indicates anagramming the letters.
'beers' becomes 'ales' (ale is a type of beer).
'out' indicates putting letters inside.
'rents' anagrammed gives 'rtnes'.
'rtnes' put into 'ales' is 'ALERTNESS'.
'in' acts as a link.
(Other definitions for alertness that I've seen before include "State of vigilance and watchfulness" , "Wakeful characteristic" , "Showing attentive nature" , "It's needed to respond quickly to danger" , "Watchful state" .)