The mean-field games framework was developed to study problems with an infinite number of rational players in competition, which could be applied in many problems. The formalized study of these problems has begun, in the mathematical community by Lasry and Lions, and beside them, but independently close to the same time in the engineering community by P. Caines, Minyi Huang, and Roland Malhamé. Since these seminal contributions, the research in mean-field games has grown exponentially, and in this work we present a regularity to a case of mean-field games using particulars techniques. In this work, we study time-dependent mean-field games in the subquadratic case, that is, mean-field games, which are written as a system of a Hamilton–Jacobi equation and a transport or Fokker–Planck equation, where The Hamiltonian presented on the Hamilton–Jacobi equation has a subquadratic growth. We begin by assuming ten assumptions, and then, under these assumptions derive Lipschitz regularity of the system.