Put a brake on Coot's drunken arrests (5)
I believe the answer is:
limit
'put a brake' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'coot's drunken arrests' is the wordplay.
'coot's' becomes 'I'm' (I am - where the crossword setter is 'Coot').
'drunken' becomes 'lit' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'arrests' means one lot of letters goes inside another (inserted letters are held or arrested).
'im' going into 'lit' is 'LIMIT'.
'on' acts as a link.
Can you help me to learn more?
(Other definitions for limit that I've seen before include "border" , "end" , "Restrict to specified range" , "Furthest bound" , "Furthest point" .)