The first is the Enfield Tennis Academy, where athletically gifted boys and girls (but mainly boys) are drilled in physical and mental preparation for what’s known as The Show, a stab at professional tennis. Among the former cohort is Hal Incandenza, a star student, teen-age tennis prodigy, secret marijuana addict, and Hamlet manqué. His father, James, an experimental filmmaker and the school’s founder, has killed himself via a MacGyvered microwave oven. Much, in other words, is rotten in the state of the Enfield Tennis Academy, or E.T.A. In “Infinite Jest,” he’s going for the least solipsistic rendering of humanity he can pull off, via more than a hundred borrowed selves.