Warning: beer can start to get round resistance (8)
I believe the answer is:
alerting
'warning' is the definition.
(I know that alerting is a type of warning)
'beer can start to get round resistance' is the wordplay.
'beer' becomes 'ale' (type of beer).
'can' becomes 'tin' (both are metal containers).
'start to' suggests taking the first letters.
'round' indicates putting letters inside.
'resistance' becomes 'r' (electronics abbreviation).
The first letter of 'get' is 'g'.
'ale'+'tin'+'g'='aleting'
'aleting' placed around 'r' is 'ALERTING'.
(Other definitions for alerting that I've seen before include "Notifying" , "Warning" .)