I’m surprised I don’t hear of this happening too often.  The type of gap this fan fell into is the same type of gap that exists in right field at Chase Field between the stands and the fence.  This is an unfortunate event that took place.  I’ve posted video as capture by the A’s broadcast this evening.  I will warn you that although you do not see the fan hitting the ground, you do see him attempting to grab the foul ball and then subsequently falling.