Fall into (5)
I believe the answer is:
incur
'fall into' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for incur that I've seen before include "Become liable to (eg, a penalty)" , "Become responsible for" , "Run up" , "Bring on as a consequence" , "Become subject to (something unwelcome)" .)