Dog crazy with pep (7)
I believe the answer is:
whippet
'dog' is the definition.
(whippet is a kind of dog)
'crazy with pep' is the wordplay.
'crazy' indicates anagramming the letters.
'with'+'pep'='withpep'
'withpep' anagrammed gives 'WHIPPET'.
(Other definitions for whippet that I've seen before include "dog class?" , "Dog similar to a greyhound" , "racing animal" , "Fast runner" , "Greyhound relative" .)