One's wearing orange pants? Run! (8)
I believe the answer is:
organise
'run' is the definition.
(run can mean to organise or control something)
'one's wearing orange pants?' is the wordplay.
'one's' becomes 'I's' (Roman numeral).
'wearing' means one lot of letters goes inside another.
'pants?' indicates an anagram (UK informal term for 'nonsense' or 'rubbish').
'orange' with letters rearranged gives 'organe'.
'is' put inside 'organe' is 'ORGANISE'.
(Other definitions for organise that I've seen before include "Arrange and co-ordinate activity" , "Plan, direct, co-ordinate" , "Arrange, plan or direct" , "Arrange in a systematic or orderly way" , "Onagers I manage to make arrangements for" .)