I guess to me it's different because it's not a defined boundary, with lines you can see... Right? Like the ref at a basbetball game can't say "I feel the free throw line is 3" closer to the basket" and change the physical location of the free throw line, but an ump for a baseball game can say "I feel the strike zone is 3" to the left" and that makes it so. The strike zone is, by nature of the umps, arbitrary, while the position of lines on a rink or court are not.