Instructor has run to unknown betrayal (9)
I believe the answer is:
treachery
'betrayal' is the definition.
(I know that betrayal can be written as treachery)
'instructor has run to unknown' is the wordplay.
'instructor' becomes 'teacher' (synonyms).
'has' is an insertion indicator.
'run' becomes 'r' (cricket abbreviation).
'to unknown' becomes 'y' (algebra).
'teacher' placed around 'r' is 'treacher'.
'treacher'+'y'='TREACHERY'
(Other definitions for treachery that I've seen before include "disloyalty" , "Double-dealing" , "Treason" , "Betrayal of trust" , "Deceptiveness" .)