(CNN)The English Premier League has long been decided by the finest of margins; a dropped point here, a missed goal there.
Just a single point separated last year's champion Manchester City from runner-up Liverpool and, as Jurgen Klopp's side are now learning, languishing mid table, chances to win the title do not come around often.
So when "human error," as acknowledged by the body responsible for Premier League referees, allowed Brentford's equalizer to stand in a 1-1 draw with league leader Arsenal, it provoked a furious reaction as it denied the Gunners a crucial victory.
"I just looked back and it is offside, yes," manager Mikel Arteta told Sky Sports afterwards. "Have they explained why it wasn't allowed? No. It is frustrating but they will probably give an explanation later in the week. Today we haven't got one."
With Brentford trailing 1-0, Ivan Toney headed in a goal after the ball had bobbled around the penalty box from a free kick.
The Video Assistant Referee (VAR) Lee Mason checked Ethan Pinnock's challenge on Gabriel during the initial free-kick but appeared to not use the VAR guidelines to check a second incident in the goal's build up when Christian Norgaard seemed to be offside.
Arsenal sits top of the Premier League.