Athletic event: come prepared with a gymslip (7,5)
I believe the answer is:
olympic games
'athletic event' is the definition.
'Olympic Games' can be an answer for 'event' (Olympic Games is an example). I am not sure about the 'athletic' bit.
'come prepared with a gymslip' is the wordplay.
'prepared with' indicates an anagram.
'a'+'gymslip'='agymslip'
'come' anagrammed with 'agymslip' can make 'OLYMPIC GAMES'.
Can you help me to learn more?
(Other definitions for olympic games that I've seen before include "Two thousand and twelve London event" , "Event whose sign here" , "International sporting event" , "International athletic event" , "Four-yearly event" .)