Why does Gene hit Quackenbush? What could be the hidden reason?

Gene goes to crew practice, which is run by Quackenbush, the uniformly disliked crew captain. Gene is assistant captain, and not on the team; Quackenbush immediately challenges him, not trusting Gene because of his non-participation in school sports other than to manage and help out. They have a fight, and both tumble into the water; Quackenbush tells him to get lost, and he does.

Again, Gene is seen as identifying with Finny to the point of taking on Finny's struggles and sympathizing with him by sharing Finny's physical limitations. Gene feels that in his argument with Quackenbush, he is somehow defending Finny, though Finny is in no way involved; Gene feels that he has become "Finny's defender," and seems to take the role very seriously. Perhaps out of guilt for hurting Finny, Gene sympathizes with him by not participating in sports, as if he had a shattered leg as well. Perhaps Gene wants to take on Finny's burdens, out of guilt for wronging his friend; and perhaps it is part of Gene's denial of his wrongdoing, another theme of the book. After the accident, Gene's jealousy and suspicion disappear almost completely, as he begins to bond himself to Finny; and, also out of a sense of guilt-born obligation, Gene agrees to serve as Finny's surrogate in the realm of sports, and participate as best he can in place of his friend. Gene confesses that his purpose in hurting Finny might well have been "to become a part of Phineas"; however, this may be another distraction from Gene's real issue of his malicious actions, as Gene has continued to ignore such a serious question in his denial after the accident.