The most common and most likely answer to this crossword clue is the 8 letter word COCKAPOO
I've seen this crossword clue in The Times
C
O
C
K
A
P
O
O
Buddy explains!

The straight part
We know that "entrant for Crufts?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case entrant for crufts? = cockapoo.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does COCKAPOO mean?
COCKAPOO noun- A cross between an American cocker spaniel and a miniature poodle.