Skippers sat up eating in after international (8)
I believe the answer is:
captains
'skippers' is the definition.
('captain' can be a synonym of 'skipper')
'sat up eating in after international' is the wordplay.
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'eating' means one lot of letters goes inside another.
'after' says to put letters next to each other.
'international' becomes 'cap' (sportsperson who competes internationally).
'sat' reversed gives 'tas'.
'tas' going around 'in' is 'tains'.
'tains' after 'cap' is 'CAPTAINS'.
(Other definitions for captains that I've seen before include "Leads (a team)" , "Commanders, naval say" , "Leading men" , "Commanders of troops" , "Officers, in command of ships say (8)" .)