The revised offside law for the new season states “A player in an offside position shall be penalised if he makes an obvious action which clearly impacts on the ability of an opponent to play the ball.”
A case in point is Juan Mata’s goal against Stoke City last season.
Marcos Rojo from an offside postition made an attempt to head the ball past the Potters goalkeeper Asmir Begovic – ‘an obvious action’ to play the ball.
He did not make contact and so the according to the old rules the goal was allowed.
According to the new rules it would have been disallowed.

It’s going to make for more contentious contentions than ever before..!
More detailed analysis of the rule here…