NCAA obs
 

Game 1 of Tennessee @ Arkansas.

R1 at 2nd. Ball hit to F8 who throws home. F2 has back foot in front of the plate as she receives the throw. R1 swung wide around third and is sliding towards a spot approximately two feet behind the plate and is reaching to touch the plate with her hand.

.The catcher drops to her knee beside the plate (the portion parallel to the batter's box) spins and reaches to touch R1's body. (ie... there is a clear path to at least half of the plate)

As the tag is applied, F2's arm "blocks" R8's arm from reaching the plate. Glove touches R8's body and ump rules "out".

Replay official rules obstruction, "safe".

Trying to wrap my head around this... I do not know what else F2 could do and still make a play.

Disclaimer, NFHS/USA, not an NCAA umpire.

Usually, "still make a play" does not matter in the rule.

Is "F2 has back foot in front of the plate as she receives the throw" the OBS that was called?

The broadcast crew had no clue (as usual) and the ump gave no explanation.

From the OP, it appears to me that any potentially obstructing act took place after the ball was received.
Therefore no obstruction.