In traffic, one long angry attack (6)
I believe the answer is:
tirade
'long angry attack' is the definition.
'tirade' can be an answer for 'attack' (thesaurus). I am not certain of the 'long angry' bit.
'in traffic one' is the wordplay.
'in' means one lot of letters goes inside another.
'traffic' becomes 'trade' (traffic can mean illegal trade).
'one' becomes 'i' (Roman numeral).
'trade' going around 'i' is 'TIRADE'.
Can you help me to learn more?
(Other definitions for tirade that I've seen before include "Prolonged abusive speech" , "String of invective" , "Furious denunciation" , "Fulmination" , "A long, vehement harangue" .)