On the ball, sportingly, but it's still pretty low (4)
I believe the answer is:
base
'low' is the definition.
(synonyms)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for base that I've seen before include "Mean; HQ" , "floor" , "Found - station - contemptible" , "This underlying structure" , "Ignoble; low part" .)