Well, this is a good one and one that many are not familiar with.It is indeed legal, as Posty said, and is generally referred to as the "skunk in the outfield" play.1. Runner can basically take his lead pretty much anywhere he wants -- except for taking it in a position in which to get a running start when tagging on a caught fly ball.2. The baseline is indeed established based on where the runner is when a play is made on him -- and this has nothing to do with the line between the actual bases. If the runner is in the grass area of right field and a play is made on him -- his baseline becomes a straight line between where he is then and the base (well, 3 feet on either side of that line). If he then stops and runs back to the other base, a NEW baseline is established -- from where he is then in a straight line to the base he is running toward.*The whole point of the play is generally to cause a balk, an error, or to get in a pickle play for the purpose of scoring the runner on 3rd base without having to get a hit. I've only seen it happen twice and it truly freaks out the defensive team (and the umpires, too, if they aren't skilled).So, now you've learned something today.