Leaders in Dallas Invitational set course record (4)
I believe the answer is:
disc
'record' is the definition.
(eg a CD, compact disc)
'leaders in dallas invitational set course' is the wordplay.
'leaders in' suggests taking the first letters.
The initial letters of 'dallas invitational set course' is 'DISC'.
(Other definitions for disc that I've seen before include "Layer of cartilage between spinal vertebrae" , "Protein-constituent acid" , "Circular flat structure in the spine" , "jockey may be after" , "Sound recording" .)