تعریف و معنای "[have] a dog in the (race|hunt)"

What is the origin of the idiom "have a dog in the race" and when to use it?

The origin of the idiom "have a dog in the race" can be traced back to the brutal and illegal practice of dogfighting, in which two dogs are forced to fight each other for the amusement of spectators. In this context, people who owned dogs or had placed bets on the outcome of the fight had a personal interest in the outcome. As the phrase became more widely used, it evolved to refer to any situation in which someone has a personal interest in the outcome of an event or decision.