The most common and most likely answer to this crossword clue is the 6 plus 2 plus 7 letter word SAFETY IN NUMBERS
S
A
F
E
T
Y
I
N
N
U
M
B
E
R
S
More clues leading to the result SAFETY IN NUMBERS
Buddy explains!
The straight part
We know that "assurance of one in a crowd" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case assurance of one in a crowd = safety in numbers.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.