Professional football is a results-driven game that carries a high degree of pressure and coaches are always in the firing line when things go wrong.
Arnold is showing signs of frustration after seeing his side get on the wrong side of some refereeing decisions that may have cost the Sky Blues.
But it has not been one-way traffic.
Arnold said very little but showed a dark mood after Friday night's Round 10 match against Adelaide United, which the Sky Blues lost 2-1 to a last-gasp penalty from Marcelo Carrusca after playing for an hour with 10 men due to the dismissal of Alex Gersbach.
Jacques Faty's clumsy challenge on Dylan McGowan was ruled by referee Strebre Delovski to be a penalty.
Most people, including Sydney chief executive Tony Pignata, saw it that way but Arnold seemingly would have none of it.
The coach, who declared that he would make a statement rather than take questions in the post-match press conference, congratulated the Reds and praised the grit of his side before he added the way Sydney had lost the game was "criminal" and concluded "that's pretty much all I've got to say."
Coaches can come up with any excuse to justify a bad result but that was not even a nice try, Arnie.
To imply ulterior motives behind the referee's decision to award the home team a rightful penalty was in very poor taste.
This after a headed goal from Reds striker Pablo Sanchez on the stroke of half-time was rubbed out for a dubious offside.
Arnold is a very good coach who has led his teams to three A-League grand finals - winning one championship with Central Coast Mariners and narrowly missing out on another with the same club before last season's defeat with the Sky Blues - since he joined the competition in 2010.
Those who play under him swear by his loyalty to his players, his ability to manage a group and bring results thanks to his tactical acumen.
Arnold is not the only coach who complains about this or that but he needs to tone down his anger at whoever he deems to have done the wrong thing by his club.
Two weeks ago he sent his assistant Steve Corica to face the media after a 0-0 home draw with Wellington Phoenix because he thought it was best not to risk being fined for any disparaging comments he might make.
He still got fined $1000 for not showing up, bringing his total for the last three seasons to $12,500 (with no right of appeal).
There is no doubt that Arnold is under pressure although this is coming also from himself.
But he is not the only coach in the A-League who is expected to deliver.
His Adelaide counterpart Guillermo Amor had not tasted victory for the first eight A-League matches but he never complained.
There is a growing feeling that Arnold's furious rants are a clever smokescreen, aimed at deflecting attention from the fact that the football the Sky Blues are playing, with only a few exceptions, is mediocre at best.
I do not subscribe to that view, the smokescreen bit that is.
Arnold is a proud and passionate football man who has done the hard yards to get where he is today.
He puts everything into his job and when he sees a wrong or believes that a wrong has been done to his teams he will speak his mind.
He is as uncompromising and straight-shooting as a coach as he was as an Australia striker in the 1980s and 1990s.
Nothing wrong or unusual about that.
He also would feel that coaches' destinies are too often determined by other people such as referees and he's not prepared to accept that as part of the game and take it on the chin as some other coaches might prefer to do.
It's just that he needs to accept that referees' bad calls usually even out.
And that occasionally the refs might just get it right too.
FOOTNOTE: Arnold has denied he ever said the penalty decision in Adelaide was wrong. He said he used the word ‘criminal’ in terms of how his team had suffered a last-gasp loss after playing for more than an hour with 10 men. The World Game understands that Arnold, by using the word ‘criminal’ and his demeanour after the game, implied that he was angry with the ref’s decision.