Breaking linnet egg is irresponsible (9)
I believe the answer is:
negligent
'irresponsible' is the definition.
'breaking linnet egg' is the wordplay.
'breaking' indicates anagramming the letters.
'linnet'+'egg'='linnetegg'
'linnetegg' is an anagram of 'NEGLIGENT'.
'is' acts as a link.
(Other definitions for negligent that I've seen before include "sloppy" , "Careless, remiss" , "slack" , "Not taking due care" , "Lax" .)