Son caught by mob has to struggle (8)
I believe the answer is:
scrabble
'to struggle' is the definition.
(I've seen this before)
'son caught by mob' is the wordplay.
'son' becomes 's'.
'caught' becomes 'c' (cricket abbreviation).
'by' means one lot of letters go next to another.
'mob' becomes 'rabble' ('rabble' can be a synonym of 'mob'**).
's'+'c'+'rabble'='SCRABBLE'
'has' is the link.
(Other definitions for scrabble that I've seen before include "Struggle to gain possession" , "Grope for something - board game" , "Clabbers in popular word game" , "Popular word game using board" , "In which X=8 and Z=10" .)