Below is an excerpt from an essay on Literary Hub:
It was sweet that readers who have absolutely no pig in the race would care so much about a story that they wanted to shout it from the rooftops.
I have never come across this alleged idiom, so I turned to OED but to no avail. Results from COCA for "no pig" are rather immaterial, too. Then I searched Google for "no pig in the race", to find out that there seems to be something like pig-racing in North Carolina State Fair, but nothing relevant to the usage in the above sentence.
I was a little confused. The author of the essay above used this expression like it was an idiom, but I reckon there should be some steps away from "unfamiliar phrases you can guess upon" to an easily recognizable idiom.