Grab a nap, having necked last of beer (6)
I believe the answer is:
arrest
'grab' is the definition.
(thesaurus)
'a nap having necked last of beer' is the wordplay.
'nap' becomes 'rest'.
'having' means one lot of letters goes inside another.
'necked last of beer' becomes 'r' (I am not sure about this - if you are sure you should believe this answer much more).
'rest' going around 'r' is 'rrest'.
'a'+'rrest'='ARREST'
Can you help me to learn more?
(Other definitions for arrest that I've seen before include "Take into legal custody" , "Detain under suspicion of criminal behaviour" , "Stop, check (progress)" , "Cause to stop" , "Nab" .)