When Billy Vunipola plays well, England win. That used to be the rule of thumb. When he rocks and he rolls, Vunipola becomes such a momentum magnet that England are unstoppable.
He has long been a barometer for England's fortunes. So it follows that in the past year he has been ordinary and so have England.
What happened in Cardiff yesterday then defied convention. Billy rediscovered his punch, yet England ended up on the canvas.
The Saracens forward carried 15 times and made 94 metres - 93 more than he had in England’s previous two games. He caught the eye left, right and centre, forever in the thick of the action.
Read more on mirror.co.uk