Man eaten by pet shark (5)
I believe the answer is:
cheat
'shark' is the definition.
(I know that shark is a more specific form of the action cheat)
'man eaten by pet' is the wordplay.
'man' becomes 'he' (he refers to a man).
'eaten by' is an insertion indicator (inserted letters get eaten).
'pet' becomes 'cat' (cats are often kept as pets).
'he' inserted into 'cat' is 'CHEAT'.
(Other definitions for cheat that I've seen before include "Hoodwink" , "offending pupil" , "Play dishonestly" , "Dishonest person" , "22 [FRAUDSTER]" .)