noun, counter
Sports counter or noun for a hit or stroke with a bat, club, racket, etc. Often used in baseball, golf, and similar sports.
彼はその試合で三打数二安打だった。
He had two hits in three at-bats in that game.
ゴルフで、このホールはパー4だから、二打でグリーンに乗せたい。
In golf, this hole is a par 4, so I want to reach the green in two strokes.
打つ is the verb 'to hit'; 打 is the noun/counter form used in sports statistics and descriptions.
安打 specifically means a safe hit in baseball, while 打 is a more general counter for hits or strokes.
The kanji 打 means 'strike' or 'hit'. The reading だ is the on'yomi, commonly used in sports-related compounds.