Painter Jack's fallen off the pier (4)
I believe the answer is:
etty
'painter' is the definition.
(William Etty, 1787-1849)
'jack's fallen off the pier' is the wordplay.
'jack' becomes 'J' (playing card abbreviation).
'fallen off' suggests deleting specific letters.
'the pier' becomes 'jetty' (I've seen this before).
'jetty' with 'j' taken away is 'ETTY'.
(Other definitions for etty that I've seen before include "British artist, 1787-1849" , "English painter, William (1787-1849)" , "painter of the nude" , "English artist" .)