Nick has to come across (3,4)
I believe the answer is:
run into
'come across' is the definition.
('run into' can be a synonym of 'come across')
'nick has to' is the wordplay.
'nick' becomes 'runin'.
'has' is a charade indicator (letters next to each other).
'runin'+'to'='RUN INTO'
(Other definitions for run into that I've seen before include "Happen to meet or collide with" , "Happen to meet - with a bump?" , "Encounter (someone)" , "Encounter by chance - or collision?" , "Meet accidentally on the trot?" .)