It's hard to get as low as this (4,6)
I believe the answer is:
rock bottom
'as low as this' is the definition.
The definition suggests a singular noun which matches the answer.
'it's hard to' is the wordplay.
I cannot really understand how this works, but
'to' is found in the answer.
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is found within the answer.
This explanation may well be incorrect...
'get' is the link.
Can you help me to learn more?
(Other definitions for rock bottom that I've seen before include "worst condition possible" , "Total despair" , "such a price is heavily reduced" , "Lowest possible level" , "As low as you can get" .)