Throw out unknown factor in mixed peel (5)
I believe the answer is:
expel
'throw out' is the definition.
(I know that throw out can be written as expel)
'unknown factor in mixed peel' is the wordplay.
'unknown factor' becomes 'x' (algebra).
'in' is an insertion indicator.
'mixed' indicates anagramming the letters.
'peel' is an anagram of 'epel'.
'x' inserted within 'epel' is 'EXPEL'.
(Other definitions for expel that I've seen before include "Put out" , "Drive out, banish" , "Reject" , "Drive out - dispossess" , "Remove from membership" .)