Run across traveller (5)
I believe the answer is:
rover
'traveller' is the definition.
(rover is a kind of traveller)
'run across' is the wordplay.
'run' becomes 'r' (cricket abbreviation).
'across' becomes 'over' ('over' can be a synonym of 'across').
'r'+'over'='ROVER'
(Other definitions for rover that I've seen before include "Itinerant person" , "Car - dog" , "Wanderer, rolling stone" , "pirate ship" , "Vehicle driven remotely over extraterrestrial terrain" .)