Possibly secure the perimeter of the fracas (6)
I believe the answer is:
mayhem
'the fracas' is the definition.
(thesaurus)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for mayhem that I've seen before include "Total chaos" , "Violent destruction of confusion" , "Violent or damaging action, a crime" , "Much trouble when" , "Big trouble!" .)