Most certainly rotating in pan/crop is a good way, but if there are lots of video events that need rotation, then there's the choice of copy/pasting the pan/crop attributes to the other events or creating a track dedicated just for the upside-down video events and then use track motion in the track header to rotate 180º so that every video event placed on that track is automatically inverted.

Also available is R clicking a video event and selecting Properties from the context window that opens, then go to the Media tab where there is a field at the bottom for setting the rotation angle (inverting 180º is a preset in that field) - but this setting does not copy/paste so it would have to be done event-by-event unless you have Vegasaur which does allow selected video events on the timeline to have their properties (inc. rotation) changed as a job lot.

but this setting does not copy/paste so it would have to be done event-by-event

@pioneer109 You don't need to try copy/paste, to do individual events or use Vegasaur.

In Project Media window select all the clips that need inverting. Then on one of the clips right click for Properties, Go to the Media Pane and Rotation. Alter it to 180 Inverted and all the selected clips will change. At least this is what happens in my VP21.