give someone a run for their money

To "give someone a run for their money" means to challenge or compete with someone in a way that surprises or impresses others, even if the person or team is considered highly skilled or successful. It implies being a formidable opponent who can compete at the same level or even surpass the other person's expectations. This phrase is often used in sports, business, or any situation where one is pitted against another, suggesting that the competition will not be easily won.