Dirt caught first in casual shoe (7)
I believe the answer is:
scandal
'dirt' is the definition.
(I know that dirt can be written as scandal)
'caught first in casual shoe' is the wordplay.
'caught first' becomes 'c' (sst letter of 'caught').
'in' means one lot of letters goes inside another.
'casual shoe' becomes 'sandal' (sandal is a kind of shoe. I am not sure about the 'casual' bit.).
'c' going into 'sandal' is 'SCANDAL'.
Can you help me to learn more?
(Other definitions for scandal that I've seen before include "Subject of Sheridan's school" , "Cause of general outrage" , "It injures reputation" , "Shock" , "Rumour, gossip" .)