He's on the road with a group (4)
I believe the answer is:
herd
'a group' is the definition.
(herd is a kind of group)
'he's on the road' is the wordplay.
'on' means one lot of letters go next to another.
'the road' becomes 'rd' (abbreviation**).
'he'+'rd'='HERD'
'with' acts as a link.
(Other definitions for herd that I've seen before include "The rabble" , "Group of animals, cattle, say" , "Group of cows, elephants etc" , "Collection of cattle" , "Flock" .)