Which of you came to a stop? (4)
I believe the answer is:
whoa
'to a stop?' is the definition.
(command to stop a horse)
'which of you came' is the wordplay.
'which of you' becomes 'who' (I've seen this in another clue).
'came' becomes 'a' (I can't justify this - if you can you should believe this answer much more).
'who'+'a'='WHOA'
Can you help me to learn more?
(Other definitions for whoa that I've seen before include "Instruction to a horse to stop" , "Opposite of "Giddy-up!"" , "halt" , "Command to horse to stop or stand still" , "Stop! - steady on!" .)