The best or one of the worst things a golfer can do (3)
I believe the answer is:
top
'the best' is the definition.
(top can mean the very best)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for top that I've seen before include "Spinner" , "Highest, child's toy" , "Highest point or position" , "The circus tent can be a big one" , "Uppermost part" .)