This paper presents a Stackelberg game between the tracker and peer of a torrent in a BitTorrent community which incentivizes cooperation amongst peers. We propose a change in the allocation of peers to a peer by tracker and suggest modifications in the allocation algorithm rather than keeping it completely random. By this change the role of tracker in a BitTorrent community is promoted from just a point of contact amongst peers to a moderator of cooperation among connected peers. As leechers in BitTorrent are faced with the conflict between eagerness to download and the unwillingness to upload, we mitigate this selfish behavior by incentivizing the peers with high upload-download ratio by awarding them with more peers to connect with and we punish the selfish peers who do not contribute more than a threshold value by limiting the number of peers allocated to them. We use a game theoretic model to prove that dominant strategy equilibrium exists in such game and the strategy to achieve this equilibrium is to cooperate for each peer. We further simulate the suggested incentive mechanism experimentally using Network Simulator 2.29 and prove the effectiveness of our results.