Catch slow mover initially dropping off? (4)
I believe the answer is:
nail
'catch' is the definition.
(thesaurus)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for nail that I've seen before include "A metal pin or spike" , "Horny covering of the digits" , "Spike, tack" , "Arrest (informal) - fix" , "Perfectly execute" .)