Rover has no crackers (5)
I believe the answer is:
nomad
'rover' is the definition.
(nomad is a kind of rover)
'no crackers' is the wordplay.
'crackers' becomes 'mad' (I've seen this before).
'no'+'mad'='NOMAD'
'has' is the link.
(Other definitions for nomad that I've seen before include "Unsettled type" , "Wanderer" , "one must move on" , "A wandering tribesman" , "Person wandering" .)