It's a broad question, but defending is a broad art! Pep always says we attack in small spaces and defend big spaces, so I guess defending when exposed 1 v 1 is an essential quality that all our defenders need. Incidentally, it's one of Stones' greatest weaknesses which is why I don't have him down as being one of our first choice centrebacks (he drops off and off until the ball is in our net). So if he's good 1 v 1, that's encouraging. His height and aerial prowess is a big plus too. I think we also need defenders that are aggressive and prepared to press and intercept the ball high and early. So if he can do that too then that's smashing :)