The most common and most likely answer to this crossword clue is the 5 plus 3 plus 6 letter word TOING AND FROING
T
O
I
N
G
A
N
D
F
R
O
I
N
G
Buddy explains!
The straight part
We know that "bustling activity" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case bustling activity = toing and froing.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.