Fourteen head off touring in Transit (2,5)
I believe the answer is:
en route
'in transit' is the definition.
(I've seen this before)
'fourteen head off touring' is the wordplay.
'head off' means to remove the first letter (the first letter or 'head' is removed).
'touring' is an anagram indicator (letters move or tour around).
'fourteen' with its initial letter taken off is 'ourteen'.
'ourteen' anagrammed gives 'EN ROUTE'.
(Other definitions for en route that I've seen before include "On the way - in France" , "In transit (French)" , "on the road" , "March" , "As part of a journey" .)