What is (someone) playing at?
What is someone's agenda or ulterior motive? Why is someone doing this? I can't figure out why Janet is suddenly volunteering for a job she said she would never do. What's she playing at? What are you playing at trying to go on a date with my sister?
what’s somebody ˈplaying at?
used to ask in an angry way about what somebody is doing: What do you think you’re playing at?