Some hear a shark, disregarding danger (4)
I believe the answer is:
rash
'disregarding danger' is the definition.
(rash can mean reckless)
'some hear a shark' is the wordplay.
'some' says the answer is hidden in the clue (some parts of the word are used).
'RASH' is hidden within 'hear a shark'.
(Other definitions for rash that I've seen before include "Red area on skin" , "Impulsive - skin condition" , "Eruption on skin, imprudent" , "Eruption of spots on skin" , "complaint" .)