alastair
ignorant
You're a bit confused mate.
The linesman's primary job (in general, not officially per se) is to flag when a player is offside. The referee doesn't focus on this. When the linesman flags the referee has no reason or evidence to go against their word. Sometimes they do though.
For offsides the linesman has the decision 99% of the time for that reason. I'd imagine it's nowhere near 90% for incidents in play.
Well he's now called a "refereeing assistant." I don't know, I just know that if that goal had gone against Arsenal, I'd be fuming for days. You can argue they even themselves out though, given that Spurs scored when the assistant had his flag up at Fulham a couple of weeks back.