go to bat for someone = help out and support someone
棒球是美国人喜欢的一种运动，去帮别人击棒球，表示去帮助别人。

范例对话:
A: Is it true that Don got into some trouble at work last week?
Don上周工作上遇到了些麻烦。

B: Yes, he did. He was reproached for not turning in his sales reports, but his secretary went to bat for him.
是的。他被责备没有交销售报告，但是他的秘书帮了他的忙。

A: What was she able to do?
她能做什么？

B: She helped him out a great deal by admitting that she had misplaced the reports that he gave her to be typed.
她承认她将Don让她打的材料放错了地方，从而来帮Don解围。

A: So, it was her fault, not his.
喔，那是她的错，而不是Don的错。

B: Right.
是的。