Likely to prove the biggest pull in the athletics programme (3,2,3)
I believe the answer is:
tug of war
'pull in the athletics programme' is the definition.
'tug-of-war' can be an answer for 'pull' (thesaurus). I'm not certain of the 'in the athletics programme' bit.
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for tug of war that I've seen before include "Traditional field contest" , "Sport that uses a rope" , "Game in which two teams pull on rope" , "Long, hard struggle between groups" , "Contest of strength" .)