Dog Fighting and Language

Not sure why I started thinking about this but it occurred to me that many phrases that have their roots in dog fighting have worked their way into everyday legitimacy. For examples:

The phrase "I don't have a dog in this fight".

The saying "It's not the size of the dog in the fight - it's the size of the fight in the dog".

Finally - the everyday popular term "underdog" which I assume referred to the dog on the bottom getting the worst of it in a dog fight.

Not sure if using these terms and phrases is bad but I had to write this to get the thought out of my head.