Hoskins will go after German unit (4)
I believe the answer is:
gill
'unit' is the definition.
(gill is a kind of unit)
'hoskins will go after german' is the wordplay.
'hoskins will' becomes 'I'll' (where the crossword setter is 'Hoskins').
'go after' says to put letters next to each other.
'german' becomes 'g' (abbreviation).
'ill' after 'g' is 'GILL'.
(Other definitions for gill that I've seen before include "A little drink" , "Fish's breathing apparatus" , "Eric ---, sculptor; breathing organ" , "Organ for breathing under water" , "Small liquid measure" .)