Ambassador and a university lecturer face to face (4-2)
I believe the answer is:
head-on
'face to face' is the definition.
(as in talking to someone face-to-face)
'ambassador and a university lecturer' is the wordplay.
'ambassador' becomes 'he' (His or Her Excellency).
'and' is a charade indicator (letters next to each other).
'university lecturer' becomes 'don' (don can mean an academic - especially at Oxbridge).
'he'+'a'+'don'='HEAD-ON'
(Other definitions for head-on that I've seen before include "Collision happening in full-frontal way" , "(Of crash) involving the front of vehicle)" , "One had (anag.)" , "Frontal, collision say" , "Of car crash, full frontal" .)