Wasn't the contract already broken when six people ended up tied to train tracks?
But if I pull the lever (or pushed a fat man onto the track that would halt the train), I am the one who is responsible for the resulting death, which makes me the one who broke the contract.
That's the major dilemma here, because pulling the lever is the utilitarian-correct choice that saved more lives, but whoever pulled the lever went from being innocent to being a murderer.