In what way is chapter 11 the climax of the novel?

This chapter involves the culmination of secrets and repressed feelings. Just as Gene tries to deny responsibility for the accident, Finny tries his best to cover up his friend's guilt. They work together to try and thwart the charges that Brinker puts before them, and fully illustrate their very different natures. This is a unique occasion, because Finny cries, for the first time that Gene has been witness to, and for the first time in the book. He surrenders his will to fight, which may be partly to blame for his accident at the end of this chapter.