What event precipitates the climax of the story? How might this event have been foreshadowed earlier in the chapter?

Brinker again comes to visit the boys, usually not a good sign. Brinker is more obsessed with the accident than Gene or Finny. We just know something bad is going to happen as Brinker pushes and pushes for the truth. This precipitates the accident. Finny freaks out and runs from the room. He falls on the marble steps outside, and re-breaks his leg. I think the snowball fight where Finny gets pelted with snow may foreshadow this event.