Whips offender has sliced through geezer (8)
I believe the answer is:
flagella
'whips offender' is the definition.
'flagella' can be an answer for 'whips' (I've seen this before). I'm unsure of the 'offender' bit.
'sliced through geezer' is the wordplay.
'sliced' becomes 'lag' (I am not sure about this - if you are sure you should believe this answer much more).
'through' indicates putting letters inside (inserted letters go through the word).
'geezer' becomes 'fella' (non-standard spelling of 'fellow').
'lag' placed within 'fella' is 'FLAGELLA'.
'has' is the link.
Can you help me to learn more?
(Other definitions for flagella that I've seen before include "Runners" , "whips" .)