This whole novel can be read as allegory that uses baseball to tell a deeper universal story: heroic figure seeks his destiny and falls short due to his own failings. The novel is loaded with symbolism from psychoanalysis, Greek myth, and legends of King Arthur and his knights (get it, Knights?) of the Round Table, with some real baseball history thrown in for good measure.
Malamud said in an interview that, "I transformed game into myth, via Jesse Weston's Percival legend with an assist from T.S. Eliot's The Wasteland plus the lives of several ballplayers I had read, in particular Babe Ruth's and Bobby Feller's." (Source.)
Whew! We'll try to unpack that for you in the next section (Mythic Themes) before getting into some specific symbols.