BBC football analyst Pat Nevin examines the reasons why central defenders take longer to mature than players in other positions, and the challenges this poses for managers.

Nevin believes Everton's John Stones is on course to become one of England's best ever centre-backs - despite making some mistakes at club level over the past two seasons.

Stones, 21, played in England's 2-0 win over France on Tuesday, and was the subject of several bids from Chelsea in the summer.

Pictures courtesy of the Premier League.