No Goal Everton/Man U for Offsides

[NOVARef]

Can someone explain why this was an offside offense even though the defender played the ball? Is that the offence for offside occurred because he was affecting the play immediately at the time the ball was struck? Isn't the defender playing the ball considered in these instances?

https://www.youtube.com/watch?v=aG9TN_GCAbs

 

[one]

5 pages of it here

Everton

How can a player who is sat on the floor, obstruct the line of vison of a goalkeeper who is standing up, for a deflected shot that he was never going to save? I'd like to see a replay of to what extent De Gea's view was obstructed.

www.refchat.co.uk

 

[CanuckRef]

Also, there is no such thing as offsides.