The most common and most likely answer to this crossword clue is the 9 letter word DEDUCTIVE
D
E
D
U
C
T
I
V
E
Buddy explains!

The straight part
We know that "Explaining the logic" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case explaining the logic = deductive.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 DEDUCTIVE mean?
DEDUCTIVE adjective- Of, pertaining to, or based on deduction (process of reasoning).
- Based on inferences from general principles.