It's a fairly tight offside call. Doubt very much I'd ever be waving a colleague's flag down in normal circumstances. However, the AR was a yard behind and the flag was exceptionally late when it shouldn't have been. Maybe therefore (and who knows what went on earlier in the game), the AR had lost the R's trust either by, or at that point in time (akin to our CAR tribulations)
Sorry, at this level of officiating, it's not tight at all, it's would fall into the category of a standard call to get right.
Would be interesting to know what the Comms chat was, whether the referee told him to put it down because of the defensive touch, or there was a clarification as to the defender in the middle of the park that he'd not seen, or it was a simple 'brain fade.'
Either way as an AR, it's a major Dev in the offside box which is a heavily weighted competency, so his mark is going to be below standard.
On another note, thought that Geoff Eltringham in the middle had a bit of a shaky start. First half he was a bit close to play and awarded 2 drop balls after he was hit by the ball. He also was right on top of a late challenge by Zinkernagel from Forest and didn't even award a freekick, when it could have been a card.
His penalty award to Barnsley was spot on, he had a long think about it, then correctly gave it for a mix of a tug and trip.
Second half he improved and gave a solid performance and not blowing up for a freekick on the offside call shown was a great move.