In this case there are no capitals (5)
I believe the answer is:
lower
'in this case there are no capitals' is the definition.
'lower' can be an answer for 'case' (thesaurus). I'm not certain of the rest of the definition.
'in this case there are no capitals' is the wordplay.
'in' indicates putting letters inside.
'this case' says to hollow out the word (remove centre letters) (I've seen 'cases' mean this).
'there' becomes 'lucknow' (I've seen this before).
'are no' becomes 'o' (resembles 0 - 'no' can mean 'zero').
'capitals' becomes 'er' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'lucknow' with its middle removed is 'lw'.
'lw' placed around 'o' is 'low'.
'low'+'er'='LOWER'
Can you help me to learn more?
(Other definitions for lower that I've seen before include "Let or haul down" , "Jersey perhaps" , "Inferior - scowl" , "put down" , "Let down, being inferior" .)