Baseball score in series (4,3)
I believe the answer is:
home run
'baseball score' is the definition.
(I've seen this before)
'in series' is the wordplay.
'in' becomes 'home' ('he's in' can mean 'he's home').
'series' becomes 'run' (run is a kind of series).
'home'+'run'='HOME RUN'
(Other definitions for home run that I've seen before include "Baseball score" , "Baseball achievement" , "Achievement by a sporting all-rounder" , "In baseball, it allows batter to move through all bases" , "Good baseball hit" .)