McArthur handball and the Offside Rule

All ive read and seen on the Telly this week is how Arsenal should have had a penalty in the last minute if you look at the incident i think it should have been a free kick to us for offside.
The offside rule needs sorting out, Smackmybitchup was clearly standing in front of Ali in the lead up to the free kick and only moved at the last second this was blocking Ali’s vision so was clearly involved in the play. They did the same thing at Villa and scored from it.

So when are you on or offside?