Gianluigi Donnarumma’s lack of discipline is a problem being ignored by Pep Guardiola

They are the Premier League’s dirty half-dozen. Or its persistent offenders, anyway. As December began, six players had incurred suspensions for accumulating five cautions in different games. They are Cristian Romero, Marcos Senesi, Sasa Lukic, David Brooks, Lucas Paqueta and Kiernan Dewsbury-Hall.

The first trio seem more understandable – two centre-backs and a defensive midfielder – than the three flair players, though two of Dewsbury-Hall’s cautions were harsh at the…