Our lead singer was sick, so the guitarist did some great pinch-hitting on vocals.

pinch-hitting 来自棒球术语 pinch hit（代打），由 pinch（紧急情况）和 hit（击打）组成。在棒球中指"替补击球手"，引申为"临时顶替某人完成任务"的意思。这里指吉他手临时顶替主唱演唱。