Yeah, I noticed a poop ball on the foot as well. You need to add some bedding or some sort of litter to the floor. It keeps them out of the poop and keeps bacteria at bay and keeps the ground drier. There is nothing wrong with keeping quail on the ground, I have always kept mine on a litter floor, but you have to keep it clean. If you use some sort of bedding, you can get away with cleaning less often. With no bedding, you are asking for a lot of bacteria growth and wet conditions.
When was the last time you wormed your quail? Quail kept on the ground need to be wormed once if not twice a year. It is possible this one contracted some sort of bacterial thing as well.
They're currently not on ground. the coop i put on a set of bricks and put some wood covered with wood shavings under the run. these shavings seem to be alright. however inside the coop floor where i put shavings they have turned it into a bed of solid ground. I dont know if this is because of the food or their droppings. As for worming I have never wormed them(got them two months ago). Dont know their history