It’s been a long time since he made a base hit. He always hits homeruns.
A baseball base hit is a base hit or single in baseball terms. A 二塁打 is a double, a 三塁打 is a triple, and a homerun is something you'll learn here on WaniKani at some point if you haven't already.
This is a jukugo word that uses the on'yomi readings of the kanji. You've learned the readings for both of these kanji, so you should be able to read this word already!