Mark CMG
Creative Mountain Games
While you'd usually expect the DM to be more deeply involved in the hobby, you can have casual DMing. In the context of Encounters, for instance, you've had this program for over 5 years now, that has these neat, pre-packaged adventures where each week everyone sits down at different tables and likely plays through the same scenario. A tad railroady for the 'serious' gamer, but perfect for casual play - and casual DMing. Early in the Encounters program, you could very easily walk in 15 or 20 minutes early, read that sessions' 'encounter,' and run it with no problem. Starting with Crystal Cave, and particularly in MiBG and HotDQ, there was occasionally uncertainty which challenge the party would face which week, and you'd have to either make sure it was set up the week before, or be familiar with two or even a half-dozen or so instead of just one. But you could still be /fairly/ causal about it.
But spending the majority (almost all) of the time they devote to gaming, actually gaming? I am seeing that I definitely have a different view of what I would call a casual gamer than some others in this thread.