It's already marked with building=grandstand, which is the important part. Levi's Stadium also has a similar set of tags, but PayPal Park does not have the amenity=bench. All 3 had amenity=bench added by the same person, but only PayPal Park had it removed by someone else.

You could just remove amenity=bench from both Stanford Stadium and Levi's Stadium because they're already marked as building=grandstand.

On a side note, FIFA World Cup 2026 will be played at Levi's Stadium.