Shaking my head here at the 'just throw him in the deep end and let him get on with it' approach to Stones.
I suspect if Martinez had his way and there was a league division to put the 'reserves' in for game experience, and we had enough money to bring in an established quality centre back, Stones would be playing in that league this season.
I'm glad Martinez had the foresight on this occasion to do 'a Moyes' this summer by bringing in a player like Besic. He's a utility player and can help us out CB wise when the time comes. We need Stones long term. It's vital though that he learns and develops in a measured way. Calling him a CB at the moment - let alone our best CB - is completely bizarre. His defensive grasp of that position is lacking, to say the least.