The most common and most likely answer to this crossword clue is the 11 letter word ACQUIESCENT
I've seen this crossword clue in The Daily Telegraph
A
C
Q
U
I
E
S
C
E
N
T
Buddy explains!
The straight part
We know that "as one falling into line (" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case as one falling into line ( = acquiescent.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 ACQUIESCENT mean?
ACQUIESCENT adjective- Willing to acquiesce, accept or agree to something without objection, protest or resistance
- Resting satisfied or submissive; disposed tacitly to submit