Classical and flag paraproducts arise naturally in the study of nonlinear PDEs. While multi-parameter paraproduct has been studied thoroughly, known estimates for flag paraproducts only involve single parameter. We will state L^p estimates for a particular case of the bi-parameter flag paraproduct on some restricted function spaces. We will discuss the key ingredient of the proof - a stopping-time argument which combines information from subspaces to obtain estimates on the entire space.