Some coming back assemble in dining hall (4)
I believe the answer is:
mess
'dining hall' is the definition.
(I've seen this in another clue)
'some coming back assemble' is the wordplay.
'coming back' says the letters should be written in reverse.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'ssem' can be found hidden inside 'assemble'.
'ssem' written backwards gives 'MESS'.
'in' acts as a link.
(Other definitions for mess that I've seen before include "Where men might eat" , "Where officers eat" , "Mix-up" , "Clutter" , "State of disorder" .)