He does have time on his hands but really you'd expect him to make a mistake, learn from it and move on. Problem being he doesn't seem to be doing that, how many times has he been caught out going back to the keeper? If that was me, after getting caught once the last thing on my mind would be going back to the keeper, i'd be getting rid. Instead he keeps doing it, strikers must lick their lips every time he's on the ball because he will give it to you eventually.
At the moment he's a complete liability. A good defender is one that rarely makes mistakes, Stones makes far, far too many, some small some huge. I hope he can improve, being English, but I can't see it.