fire in (one's)/the belly
Passion and determination. I'm confident that Bill will get them to listen to our pitch—he has such a fire in the belly for this sort of work.
fire in your belly
or fire in the belly
If you have fire in your belly or fire in the belly, you are ready to do something in a very energetic and passionate way. Ian has played with fire in his belly throughout his career. He accused the candidate of lacking fire in the belly. Note: You can also say that someone has a fire in their belly or a fire in the belly. He also has a fire in his belly. `I'm passionate about what I do,' he says.