The most common and most likely answer to this crossword clue is the 7 plus 5 letter word MEXICAN WAVES
I've seen this crossword clue in The Guardian
M
E
X
I
C
A
N
W
A
V
E
S
Buddy explains!
The straight part
We know that "Signals from Javier Hernandez/repeated unrest in crowd?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case signals from javier hernandez/repeated unrest in crowd? = mexican waves.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.