Two of the symbols that emerge in Chapter 3 are sports and blitzball.
Sports are a metaphor for the war. Finny, who is a great afficionado of games of athletic skill, has a most unrealistic view on winning and losing -
"Finny never permitted himself to realize that when you won they lost...that would have destroyed the perfect beauty which was sport. Nothing bad ever happened in sports; they were the absolute good."
There is a tendency to present war as glorious in nature, with no regard for the actual barbarity and suffering it entails. The focus is on winning, with little attention paid to the carnage inflicted on others. Finny's attitude towards sports reflects this naive and incomplete view of war. It is this view that seduces Leper into joining the ranks of the military; when he discovers the truth that has been overlooked, he cannot handle it and loses contact with reality.
Blitzball is also a metaphor for the war. Finny, as the person in power, makes up the rules as he goes, and the others follow his lead virtually unquestioningly, even when his rules make no sense. This is how wars are run; the men in power over nations make up the rules, and the common man must follow them without question. What is illogical is made to seem logical by the charismatic aura of power and spin, and men do what they are told without protest, carrying out the dirty work of the war.
A third symbol that emerges is Finny and Gene's trip to the beach. The trip, against all rules, denies the reality of the war that hangs over the lives of the boys at Devon and the nation; representing the "separate peace" created by Finny (Chapter 3).