Car crashed during endlessly speedy disturbance (6)
I believe the answer is:
fracas
'disturbance' is the definition.
(thesaurus)
'car crashed during endlessly speedy' is the wordplay.
'crashed' indicates anagramming the letters.
'during' is an insertion indicator.
'endlessly' means to remove the last letter.
'speedy' becomes 'fast' ('fast' can be similar in meaning to 'speedy').
'car' with letters rearranged gives 'rac'.
'fast' with its last letter taken away is 'fas'.
'rac' placed into 'fas' is 'FRACAS'.
(Other definitions for fracas that I've seen before include "Dust-up" , "Noisy brawl" , "Brawl; scuffle" , "Bust-up" , "Dispute" .)