Longman Dictionary of Contemporary English
Wiktionary
vb. 1 (context intransitive baseball English) To bat in place of another player 2 (context intransitive idiomatic English) To do something in the place of another person who is not able to perform or is less skilled; to substitute or stand in for somebody.
Usage examples of "pinch-hit".
With the Red Sox down 9-0, the manager called the bullpen and told Hatteberg to pinch-hit.
Past Scott Hatteberg and Greg Myers, the two lefties on the bench who had thought they had the night off, rushing back through the clubhouse to the batting cage to take some practice swings, in case they are asked to pinch-hit.
So I begins to lay it on a bit thick and by the time we have consumed all of the local bug juice and most of the fruit and fish, the kid is convinced that if I am not the Second Coming, I am at least pinch-hitting that day.
He's only supposed to be pinch-hitting for her, but he sits in her office and we all know that that's the new Operating Vice-President.
That’s exactly what he’d been avoiding these past fourteen years, choosing to offset his tuition in the graduate program by managing the campus radio station, instead of becoming a TA, or pinch-hitting for profs on sabbatical.