I was probably in the minority who was pleased to see Friend's appointment to this game the reason being twofold, firstly, in my opinion Friend is a far better referee than many on here make out and secondly, I think there needs to be far more variance in the PL appointments. Obviously there's the issue of referees seeing the same teams too often but I don't like the unofficial tier system within the SG. I feel it damages progression and keeps more average referees (who only ever really get mid table clashes) in their position, blocking the progression of referees who may be able one day to take charge of the biggest games. While you can never have 20 Olivers/Taylors/Deans/Atkinsons/Marriners, a PL referee of 10+ years who cannot be trusted to take charge of a number of big games each season shouldn't be doing the job.
Regardless, Friend wasn't good last night, he correctly gave an early yellow to an Arsenal player, presumably for SPA - a good start. A few minutes later a Man United player committed what was in my opinion a 50/50 SPA foul that normally I would support a referee in warning, but not yellow carding a player. However, given he had just issued a yellow card to Arsenal for an SPA foul and for the sake of perception and game management he should have issued the Man united player a yellow card, he would not have been simply 'balancing the game' as this would have been a fully justifiable caution. The best referees in my opinion, must not only be fair (as Kevin Friend unquestionably is) but also be seen, where possible, to be fair. This was not the case in this moment and from that decision on he had players from both sides but particularly Arsenal questioning his calls ans surrounding him.
Even if this may have been partially his own making, he should have dealt more strongly with these protest - clear body language and verbal confirmation that this action is not surrounded, followed by a strongly delivered yellow card should this warning not be heeded. This did not happen and there were at least 5 times I can recall 3 or more players surrounding Friend while his body language remained quite passive.
This was true of his verbal warnings to players about foul play, while often justified, they were rushed with players often walking away as he was talking - he didn't convey control or authority as one would have hoped.
Big picture though? All yellow cards were in my opinion at least supportable, play on call for the penalty 70-30 penalty call for me but acceptable, while not desirable to play on, no major errors as VAR corrected the incorrect offside call, Xhaka a total missed incident off the ball and a missed yellow card that can be forgiven, wrong as it was, foul detection good while sometimes being a bit inconsistent - a disaster? No. A really poor performance? No. A very average performance by a referee who is capable of better? In my opinion - yes.