Campus race I organised — it's a famous competition (8,3)
I believe the answer is:
americas cup
'a famous competition' is the definition.
'americas cup' can be an answer for 'competition' (I have seen 'main competition' mean 'americas cup' so perhaps 'competition' could also mean 'americas cup'). I am not sure about the 'a famous' bit.
'campus race i organised' is the wordplay.
'organised' indicates an anagram.
'campus'+'race'+'i'='campusracei'
'campusracei' is an anagram of 'AMERICAS CUP'.
'it's' acts as a link.
Can you help me to learn more?
(Other definitions for americas cup that I've seen before include "Yachting prize" , "International match between two sailing yachts, first held in 1851" , "International yachting trophy" , "Yacht-racing trophy" , "main competition" .)