The most common and most likely answer to this crossword clue is the 12 letter word HOBBLEDEHOYS
H
O
B
B
L
E
D
E
H
O
Y
S
Buddy explains!
The straight part
We know that "clumsy" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case clumsy = hobbledehoys.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 HOBBLEDEHOYS mean?
HOBBLEDEHOYS noun- An awkward adolescent boy.