Grub loses first real hot stuff (4)
I believe the answer is:
lava
'hot stuff' is the definition.
(I've seen this in another clue)
'grub loses first real' is the wordplay.
'grub' becomes 'larva' (I've seen this in another clue).
'loses' is a deletion indicator.
'first real' becomes 'r' (1st letter of 'real').
'larva' with 'r' taken away is 'LAVA'.
(Other definitions for lava that I've seen before include "Molten rock expelled by a volcano" , "Volcanic outpouring" , "Volcanic stuff" , "Volcanic emission" , "Flowing volcanic matter" .)