Even terrier pants going after good old breed (6,9)
I believe the answer is:
golden retriever
'breed' is the definition.
(golden retriever is a breed of dog)
'even terrier pants going after good old' is the wordplay.
'pants' is an anagram indicator (UK informal term for 'nonsense' or 'rubbish').
'going after' says to put letters next to each other.
'good' becomes 'g' (abbreviation).
'even'+'terrier'='eventerrier'
'eventerrier' is an anagram of 'enretriever'.
'g'+'old'='gold'
'enretriever' put after 'gold' is 'GOLDEN RETRIEVER'.
(Other definitions for golden retriever that I've seen before include "pet?" , "canine" , "Dog" .)