Fed Rules: R1 on 3rd, 1 out.
BR hits ground ball to 2B. F4 throws home. F2 is blocking HP. R1 slows, PU left arms goes up, F2 receives ball and applies tag to late sliding R1 who is blocked from HP and never reaches the plate.
OBS was ruled but he put R1 back at 3B stating that "had there been no OBS the runner would have been out" so he is putting her at 3B.
Should R1 have been allowed to score or was protecting her back to 3B correct?