The most common and most likely answer to this crossword clue is the 5 plus 5 plus 6 letter word BLACK LIVES MATTER
B
L
A
C
K
L
I
V
E
S
M
A
T
T
E
R
Buddy explains!
The straight part
We know that "movement" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case movement = black lives matter.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.