Check one's surrounded by others (6)
I believe the answer is:
'check' is the definition.
(I've seen this before)
'one's surrounded by others' is the wordplay.
'one's' becomes 'is' (roman numeral).
'surrounded by' means one lot of letters goes inside another.
'others' becomes 'rest' (I've seen this before**).
'is' placed within 'rest' is 'RESIST'.
(Other definitions for resist that I've seen before include "Go against" , "'Withstand, fight against (6)'" , "turn down" , "Sister (anag)" , "Hold out for sister" .)