pinch hitter   (ピンチヒッター)

He made his MLB debut August 20 as a pinch hitter.

He appeared in 59 games for the Brewers, mostly as a pinch hitter.

He was also used quite often as a pinch hitter throughout his career.

designated hitter   (指定打者)

Hayes was a designated hitter for Rider.

Lind has also appeared at designated hitter and in left field.

The Orioles won that game, and designated hitter Chris Davis received the win.

leadoff hitter   (リードオフヒッター)

In his early years, Bonds batted as the leadoff hitter.

Earle Combs, the Yankees leadoff hitter, followed by drawing a walk.

For the season, in 59 games batting as the leadoff hitter, he hit .309/.356/.818.