In the past it has proved to be the beginning of the end.
When a trickle becomes a torrent, when a few angry voices swell to mob proportions and home games become an ordeal for all.
Sheffield Wednesday appear to be on the brink of that precipice at the moment.
When fans turn on the team and players are saying their style may be better suited to away games, there is a problem.
For 20 years successive Owls bosses were dogged by fan comparison with the early-90s glory of Hirst, Sheridan and Waddle.
Supporters’ collective desire for success became impatience and a pressure of expectation on players and successive managers.
Right now Carlos Carvalhal’s win percentage is the same as Gary Megson’s when he was sacked in February 2012 - though in his two-and-a-half years Carvalhal has been in charge of 125 games, twice Megson’s total.
Only Brian Laws (three years, one month) has had longer at the helm than Carvalhal since Trevor Francis was sacked after three years and 11 months in 1995.
Carvalhal is undoubtedly a talented and charismatic coach.
But despite owner Dejphon Chansiri’s admirable loyalty to his man the Portuguese needs to start weaving his magic again soon if he is to carry the fans with him into 2018.
n Sledging. It’s been going on since before Sandy Jardine was berated for swatting flies by a big-gobbed Aussie in 1932.
As England prepare to take on not 11 but 23 million Australians when the Ashes starts at the Gabba on Thursday Joe Root and his squad will know the dark arts of intimidation both as givers and receivers.
But a poor start to a series can lead to a team crumbling under the vitriol.
In that ‘Bodyline’ series of 1931/32 England were about to seal the series with a win in the fifth Test at Sydney and Jardine was at the crease when play stopped for a drinks. Australian captain Bill Woodfull was about to offer Jardine water when a voice suggested otherwise: “Don’t give the b*****d a drink. Let him die of thirst.”
Jardine lived, England won and Australia has never got over it.
Whatever is said - and there’ll be plenty - it won’t beat the Aussie who barracked England captain Jardine during that same series as he swatted the flies buzzing round his head: “Leave our flies alone, Jardine; they’re the only flamin’ friends you’ve got here.”