Football / Soccer / Calcio / Futebol / Fußball

You can't really compare goalkeepers with outfield players.

Goalkeepers have a much higher reach than any outfield player, but in exchange they can't use their arms to balance their body or protect it. That makes keepers a lot more vulnerable in the air than outfield players. Their height will often cause situations where there's a high risk of the opposing player tipping the keeper over by cutting underneath him.

For me it's quite simple. If the GK had hit Robertson with his knee, it would've been a foul. In reality Robertson was hit sideways. The injury is also completely irrelevant to how the GK played.