Symbolism, Imagery, Allegory
You get the idea. This is a big story, about much more than baseball. Some literary critics thought that baseball was too trivial a subject to carry the weight of all of Malamud's added myth and symbolism (Source). Shmoop's suggestion? Ask your grandparents to tell you what they remember about the legendary ballplayers they heard about from their parents.
Babe Ruth, Shoeless Joe, Lou Gehrig, Ty Cobb—all players whose stories still have a kind of larger-than-life quality.
Maybe you feel the same way about Derek Jeter or Jackie Robinson or Willie Mays. Roy Hobbs was meant to remind us of those guys, guys who could take us out of our everyday world and remind us that heroes still exist. Play Ball!