pinch-hitting; pinch hitter
Baseball term for a substitute batter. Also used metaphorically for a substitute in other contexts.
In the bottom of the ninth, a veteran player was sent in as a pinch hitter.
He hit a home run as a pinch hitter.
Extended use: someone who performs a duty or role in place of another person, often in business or formal settings.
Because the president suddenly fell ill, the vice president attended the meeting as a substitute.
He was entrusted with the presentation as a last-minute stand-in.
The manager sent in a pinch hitter in the ninth inning.
She stood in for me when I had a sudden business trip.
He came in as a pinch hitter and hit a go-ahead home run.
ピンチヒッター is the English loanword used almost exclusively for the baseball sense of a pinch hitter, while 代打 is the native Japanese term that also extends to non-baseball substitution.
代理 is the broad business/legal term for acting as someone's proxy or agent, whereas 代打 keeps a stronger sense of stepping in for a single, specific task, often borrowed from its baseball origin.
pinch hitter
Compound of 代 (substitute) and 打 (hit, strike). Originally a baseball term, later extended to general substitution.