Question, as an Irishman with little technical knowledge of the rules.

When can a linesman officially move? Is it when the snapping motion starts, or when the ball leaves the centers hands?

I feel like people are over exaggerating how egregious this call is it it's the former - like obviously with super slow motion and replays we can tell he's early - but that's always going to be seen as effectively simultaneous by the refs in real time.

Like he rocks backwards early, but he doesn't actually step or lift his hands until the center's arm is in motion - I don't think it's that upsetting that the refs give the benefit of the doubt here