Boat crew supporting wide load (6)
I believe the answer is:
weight
'load' is the definition.
(I have seen 'Heavy load ' mean 'weight' so perhaps 'load' could also mean 'weight')
'boat crew supporting wide' is the wordplay.
'boat crew' becomes 'eight' (I've seen this before).
'supporting' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'wide' becomes 'w' (abbreviation e.g. in cricket).
'eight' put after 'w' is 'WEIGHT'.
(Other definitions for weight that I've seen before include "Feeling of oppression; heaviness" , "Import" , "Relative heaviness" , "Something to lose" , "Importance, oppressive force" .)