Sounds like a wreck to me from your description.

In that case, as long as the fielder tags the runner, I have an out.

I suspect that the umpire must have indicated and called obsruction on this play, therefore awarding the runner home.

To me that would be the only way that the umpire could rule the runner safe at home.

Hope this helps.

After everyone's response (thanks very much, by the way) and a little research in the ASA rule book, I think the PU invoked R4.10 since he too judged it as a "wreck" and not OBS or INT:

During a live ball situation, when a player becomes injured, and in the umpire’s judgment requires immediate attention, the umpire shall call “DEAD BALL”. EFFECT: Award any bases that would have been reached.

Okay, think of it this way.

If the player was just receiving the ball at the time of the collision, the defender did NOT have possession of the ball as required by 8.5.B.4. That is, by rule, obstruction.

The defense's poor play caused the runner to be injured and not reach the plate. Barring 4.10, why would any consideration be given to anything which would be a possible reward to the defense for poor play?