"Vs." vs./v. "V." [duplicate]

Possible Duplicate:
How should I abbreviate “versus”?

I came across this sentence the other day:

In the case Lee v Knapp,...

And I was a bit confused, because shouldn't it be "vs."? I looked up the dictionary and it gave "vs.", as well as "v.". So my question is, which one is better/ more correct, and if so why? Would people understand you better if you used one or the other?

It is pretty standard in the legal world to refer to cases as Plaintiff v. Defendant. This includes even when speaking the name of a case: “plaintiff vee defendant”. For example, the landmark U.S. Supreme Court case regarding abortion, Roe v. Wade, is usually called “Roe vee Wade” when spoken, not “Roe versus Wade.”

In most other cases where you would abbreviate the word versus, such as in sporting matches, you would use the two-letter abbreviation vs.