I was thinking "chemical spill" or "dumping". Things like motor oil will kill plants.
Or someone might have just dumped some household chemicals onto the lawn, while packing to move out. But wow! imagine dumping right on your own front lawn! I hope it was just the piled leaves.
Probably just wait to see if it keeps going away. Or, if you're sure you have good drainage, watering those spots a little more than you would otherwise could help leach any chemicals away. And it would probably pamper the grass and help it recover from whatever the stressor is. But I'm not experienced with turf in hot, dry climates.
