Using a mix of macro, pico, femto and relay cells, Heterogeneous Networks (HetNets), or Small Cell Networks (SCN), are likely to provide a better spectral efficiency per unit area at a lower cost. However, advanced techniques are required to handle the inter-cell interference and deliver the full benefits of such networks. In this paper, we investigate the problem of spectrum sharing in a HetNet composed of a macrocell and several femtocells. We propose a new approach in which macrocell and femtocells can share simultaneously the available bandwidth while avoiding intra-tier interference and helping the macrocell to offload by expanding the cell range of some femtocells. Our approach is formulated as a Stackelberg game in which the macrocell is selling bandwidths to femtocells in exchange of some victim macro-users to serve, mainly the macro-users who undergo severe interference from the neighboring femtocells. We demonstrate that our game theoretic converges to the stable state called Stackelberg Equilibrium analytically and by simulations. More importantly, we show that overall network performance is improved in terms of total femtocells' throughputs and spectral efficiency of the macro-users who are in the vicinity of the femtocells.