Target a rearranged event on water (7)
I believe the answer is:
regatta
'event on water' is the definition.
'target a rearranged' is the wordplay.
'rearranged' is an anagram indicator.
'target'+'a'='targeta'
'targeta' anagrammed gives 'REGATTA'.
(Other definitions for regatta that I've seen before include "Race meeting for boats" , "Rowing or sailing event" , "Boat race meeting" , "Boat racing event" , "Aquatic activity" .)