Endless sport leading to graduate getting low grade? (5)
I believe the answer is:
gamma
'low grade?' is the definition.
(academic mark lower than alpha or beta)
'endless sport leading to graduate' is the wordplay.
'endless' means to remove the last letter.
'sport' becomes 'game' (I've seen this before).
'leading to' means one lot of letters go next to another (some letters go before or lead others).
'graduate' becomes 'ma' (abbreviation for Master of Arts).
'game' with its final letter taken away is 'gam'.
'gam'+'ma'='GAMMA'
'getting' is the link.
(Other definitions for gamma that I've seen before include "Poor mark" , "Greek letter - type of rays" , "The Greek g, third in alphabet" , "Greek character" , "Letter after alpha, beta" .)