have a dog in this fight

To have some vested interest in or something to gain by a given situation. Often used in negative constructions. A: "Are you going to watch the big game tonight?" B: "Nah, my team's not playing, so I don't have a dog in this fight." A lot of people think the tax proposal only affects large multinational corporations, but many small business owners will end up having a dog in this fight. You don't have a dog in this fight, so why do you care about the outcome of this lawsuit?