the last obstruction post ever(just kidding)

[Smiley]

You call the obstruction when it occurs by signalling a delayed dead ball and verbally stating "obstruction". As soon as the runner is put out before reaching the base that would have been reached had there been no obstruction, you kill the play. In your sitch, if you believe the runner would have reached third safely had she not been obstructed, you kill the play and award bases. If you believe she would have been out at third regardless, let the play go.