Dog suddenly can't move front legs after playing. What should I do?

Thanks for using Petco Pet Education Center, formerly Petcoach! I’m so sorry to hear Pippy is having issues. I would recommend she be evaluated by her regular veterinarian as soon as possible, as an inability to move her legs can be a sign of a serious underlying issue. There are a variety of causes for what you are seeing, such as an infection (Lyme disease), neurological or orthopedic issue, among others. As some of these may be time sensitive, I would recommend she be evaluated as soon as possible to see what may be going on, and any treatment she may need. Good luck!