He's good at playing infield.
彼は内野の守備が上手い。
He is good at infield defense.
打球が内野を抜けて外野へ転がった。
The batted ball went through the infield and rolled into the outfield.
打球は高い内野フライになった。
The batted ball became a high infield fly.
The batter hit a ground ball to the infield and was out.
内野 is the infield near the bases, while 外野 is the outfield beyond it.
Compound of 内 (inside) and 野 (field), directly describing the inner part of a baseball field.