Do better at baseball, say? (3)
I believe the answer is:
cap
'do better' is the definition.
'cap' can be an answer for 'better' (both can mean to beat somebody else's attempt). I am not sure about the 'do' bit.
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for cap that I've seen before include "Beat; upper limit" , "One on head; excel" , "Limit (prices)" , "Surpass with headwear" , "Protective lid" .)