Second best bar (4)
I believe the answer is:
stop
'bar' is the definition.
(bar can mean to stop or prevent)
'second best' is the wordplay.
'second' becomes 's' (common abbreviation).
'best' becomes 'top' (top can mean the very best).
's'+'top'='STOP'
(Other definitions for stop that I've seen before include "Discontinue (an action)" , "Close < finish" , "This watch is used to time races" , "Prevent - desist" , "Pack it in - bar" .)