1
general::
Phrase(s): go to bat for someone
Fig. to support or help someone. • I tried to go to bat for Bill, but he said he didn’t want any help. • I heard them gossiping about Sally, so I went to bat for her.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
Take the side of, support, defend. For example, Dad will always go to bat for his kids. This term originated in baseball, where it means simply substituting for another batter, but it is the idea of helping one's team in this way that has been transferred to more general use. [Slang; early 1900s]
American Heritage Idioms