Lock up young man supporting African warriors without resistance (8)
I believe the answer is:
imprison
'lock up' is the definition.
(I've seen this before)
'young man supporting african warriors without resistance' is the wordplay.
'young man' becomes 'son'.
'supporting' means one lot of letters go next to another (in a down clue, some letters go below others).
'african warriors' becomes 'impi' (term for a Zulu army).
'without' is an insertion indicator ('without' can be similar in meaning to 'outside').
'resistance' becomes 'r' (abbreviation).
'impi' enclosing 'r' is 'impri'.
'son' put after 'impri' is 'IMPRISON'.
(Other definitions for imprison that I've seen before include "Confine" , "Purveyor of blooms" , "Bang up" , "Incarcerate" , "Detain" .)