Frothy stuff subsequently outside hospital (6)
I believe the answer is:
lather
'frothy stuff' is the definition.
The answer and definition can be both related to change as well as being verbs in their base form.
Maybe you can see a link between them that I can't see?
'subsequently outside hospital' is the wordplay.
'subsequently' becomes 'later' (subsequently means later on).
'outside' means one lot of letters goes inside another.
'hospital' becomes 'H' (abbreviation for hospital).
'later' placed around 'h' is 'LATHER'.
Can you help me to learn more?
(Other definitions for lather that I've seen before include "Froth formed by soap and water" , "stew" , "Foamy soap as for shaving" , "Soapy froth" , "starting to run in a sweat" .)