Applicants accepted to a law school are expected to deposit and register for classes the year (semester) in which they are accepted. It does happen that a deferment is necessary or desirable. The granting of a one-year deferment depends on the law school with responses ranging from almost always granting one to almost always never granting one. Note that if you are admitted from a waiting list, your chances of a deferment will usually not be very good. The granting of a deferment for more that one year is not very likely although some law schools will grant requests for a two-year deferment to someone participating in program that requires a two-year commitment (e.g. Teach For America). Even if a deferral is not granted, there is almost always the option of reapplying for admission at a later date.
MAKING A CAREER CHANGE
What if you graduate law school and decide that you do not want to be a lawyer? Check out the Pre-Law Handbook of New College; it offers ALTERNATIVE CAREERS FOR LAWYERS (scroll down to Chapter 9).