Space, supporting Pulp, get really big, really quickly (8)
I believe the answer is:
mushroom
'really big really quickly' is the definition.
I can't judge whether this definition defines the answer.
'space supporting pulp' is the wordplay.
'space' becomes 'room' (enough space or room to do something).
'supporting' says to put letters next to each other (in a down clue, some letters go below others).
'pulp' becomes 'mush' (I've seen this before).
'room' after 'mush' is 'MUSHROOM'.
'get' is the link.
Can you help me to learn more?
(Other definitions for mushroom that I've seen before include "develop rapidly" , "Grow rapidly" , "Grow very fast" , "Fleshy fungus" , "Rapidly increase; fungus" .)