Hundred yobs in strikes (6)
I believe the answer is:
clouts
'strikes' is the definition.
(clouting is a kind of striking)
'hundred yobs' is the wordplay.
'hundred' becomes 'c' (Roman numeral).
'yobs' becomes 'louts' (I've seen this before).
'c'+'louts'='CLOUTS'
'in' acts as a link.
(Other definitions for clouts that I've seen before include "strikes" , "Blows, cuffs" , "Patches" , "Blows, perhaps around the ears" , "Informal blows" .)