What if someone spawns on the runway after you spawn and are sitting there?
If both are spawning (after each other), they're friendlies, and don't collide.
If the field did change sides between the two planes spawning, the first one is dead by the ack that rebuilds on capture.
There can be the case of an enemy plane landing at a deacked field. This usually only happens when someone is out of fuel, and in that case usually cannot taxi to the spawn point. Also, such fields are vulched, and no-one ups. So it doesn't really matter what happens.
Of course there's the secret gamey tactic to kill the VH, deack the field, and then land one plane on each of the spawpoints. Has this ever been attempted?