100 yobs coming to blows (6)
I believe the answer is:
clouts
'blows' is the definition.
(I have seen 'Informal blows ' mean 'clouts' so perhaps 'blows' could also mean 'clouts')
'100 yobs coming to' is the wordplay.
'100' becomes 'c' (roman numeral).
'yobs' becomes 'louts' (I've seen this before).
'coming to' says to put letters next to each other.
'c'+'louts'='CLOUTS'
(Other definitions for clouts that I've seen before include "Blows, perhaps around the ears" , "Patches" , "Informal blows" , "strikes" , "Blows, cuffs" .)