The French yell, 'Attack!' (4,3)
I believe the answer is:
lash out
'attack' is the definition.
(I've seen this before)
'the french yell' is the wordplay.
'the french' becomes 'la' ('the' in French).
'yell' becomes 'shout' (synonyms).
'la'+'shout'='LASH OUT'
(Other definitions for lash out that I've seen before include "Attack with blows or words - using whip?" , "Become suddenly aggressive" , "unprovoked attack" , "Vigorously attack" , "Strike (or spend) wildly" .)