[UMP25]

OBR does adopt some NFHS interps. when things are unclear. Regardless, you are looking at this the wrong way. Again, you're thinking is too linear. It is simple to think about "past first or third base." However, just where does this demarcation end? How far "in" does the ball have to go toward the shortstop position or second baseman position before one stops thinking about "past first or third base." So if a ball rolls toward first, goes "past" it on just to its left (second base) side, it's fair, but if it rolls toward the second baseman it can be foul if it somehow spins back into foul territory? Hogwash.

The entire concept of the diagonal of the square was devised to help provide some point of demarcation past which the ball is fair regardless of where it eventually ends up. Think of it this way: if you picture a straight line from home to first/third, it's 90 feet. Now take this same line and swing it, so to speak, to the other corner base. As you begin to swing it, keeping it straight, it doesn't disappear; rather, it--roughly speaking--extends to the aforementioned diagonal. Granted, it's not exact, since this diagonal is about 63.69 feet (one half of [90 X radical 2]) away, but it's used to make it easier to determine fair/foulness.