Boxer in training, possibly has splendid start with breakfast item (7)
I believe the answer is:
skipper
'boxer in training possibly' is the definition.
(boxers often train with skipping ropes)
'splendid start with breakfast item' is the wordplay.
'start with' says to take the initial letters.
'breakfast item' becomes 'kipper' (kippers might be eaten for breakfast).
The first letter of 'splendid' is 's'.
's'+'kipper'='SKIPPER'
'has' is the link.
(Other definitions for skipper that I've seen before include "who makes short hops" , "Chap aboard trawler" , "girl with rope?" , "Captain of team or boat - type of butterfly" , "Head" .)