[greymule]

Because it is treated like a force in all circumstances by ASA. I seem to recall that it is the ASA interpretation that the BR who overruns 1B can re-instate the force by overrunning back in the other direction toward home. IOW, the defense can retire the BR in that circumstance by merely tagging the base. I don't have time now to try to look this up... does anyone else remember this? We discussed it a year or two ago on this board.

That's right. ASA, unlike other codes, considers the BR to have "occupied" a previous base—home. The BR can in fact reinstate the force by retreating (though he wouldn't have to overrun 1B; he could simply stop on the base and then retreat). Therefore, in ASA the out on the BR at 1B is indistinguishable from a force play and should rightly be termed such.

Since the rule change, I have treated the entire white/orange slab of the safety base as usable by either fielder or runner once the BR touches (or crosses 1B).