Put your shirt on somebody/something
Definition 1 of 1
Pro Tip 1/3Confidence Expression
Used to express a high level of confidence in an outcome or someone's abilities. 
She always wins these competitions, so I'd put my shirt on her any day.
Pro Tip 2/3Not Literal
The phrase is figurative and does not involve actual shirts or betting. 
Even with his injury, I'd put my shirt on him to return stronger than ever.
Pro Tip 3/3Informal Usage
It's an informal expression often used among friends or in casual conversations. 
The weather looks promising for the picnic—I'd put my shirt on it.