The authorities have decided that hair pulling is a red car offence, I don't think it's specifically mentioned in the Laws. But if it's referenced, it has to be taking into account if it's Violent conduct or Serious foul play. In this instance its neither and for a referee to regard it as such means they shouldn't officiate football games. You can't just assume that hair pulling is a deliberate act with intent to injure the opponent, a bit like handball isn't always deliberate. Keane yesterday could have broke Doku's leg, but gets a yellow. If anything the Wolves player should have got a yellow for feigning injury which IS referenced in the laws. PGMOL have made a massive error, combining hair pulling with violent conduct and no context is wrong in every sense