Obstruction again -

[Dinger]

Question - this was a high school game. Runner at 2nd - ball hit in the gap between CF and LF - shortstop runs into the runner as she is halfway between 2nd and 3rd - causing runner to stumble (ball is still in the air) - official signals the delayed dead ball obstruction signal. Runner advances toward home and is thrown out at the plate. Official ruled that she was out - no effect from the obstruction. Is this right? If this is correct, what would stop a SS from grabbing a runner to avoid allowing the winning run?