While footballers and other men (but never true gentlemen) do it as a matter of course, and unconsciously, it will always remain a real mystery to women – despite the explanation that follows – why the male homo sapiens persists in the unappetising habit of spitting on the ground. 

During the interview phase of ritualised combat, which the English-speaking world sometimes refers to as "the woof", the aim is to impress the victim so profoundly that a fight and its always attendant risks will not occur in the first place, or that any fight will be one-sided and therefore without risk to the attacker.
One particularly suitable but disgusting method favoured by aggressors is to spit on the ground in front of them, or, even more revoltingly, to spit directly into the victim’s face.

This spitting has its roots in primeval history, and has two evolutionary purposes:
Firstly, it is a way of marking one’s territory, and in wet weather a more lasting one than urinating. It shows anyone who dares to intrude: "Beware, this is the territory of a particularly healthy and strong male with bacterially uncontaminated saliva."
Secondly, it shows an intimidating wildness and strength, and not only because it demonstrates an appalling breach of civilised manners.

Before actual physical combat commences, it is normal for most contenders to have a dry mouth owing to the cocktail of adrenal hormones that is coursing through their bodies.
So by spewing out a hopefully large quantity of saliva, our aggressor is demonstrating that he is not afraid.
What is more, like a nouveau riche who lights his cigarette with a banknote, he is showing that he has plenty of a precious commodity, either money or in our case spittle.
Prior to this, the thug has abused his victim and done his best to convince him verbally that he has no chance. The other party may be suitably convinced or maybe not. So now he provides non-verbal back-up for his assertions. By adopting a wide-legged stance in front of the victim, he e.g. shows him that his genitals are proof against a potential kick by the victim, or that the victim dare not kick him anyway.
By wasting his precious saliva, and without being conscious of it, the thug provides the final proof that he is not the slightest bit under stress!
I take my reference from a hypothesis put forward in 1975 by the Israeli biologist Amotz Zahavi – one that is clearly still debated hotly is specialist circles. Since deception and fraud are by no means uncommon in nature, Zahavi opines that incontrovertible proof is needed.
The lion does not automatically believe the gazelle’s claim that it is so healthy and fast that it cannot be caught, for there are liars and cheats in the animal world as well.
If it turns out during the subsequent chase, which consumes many calories, that the gazelle is after all too fast for him, both have expended their energy unnecessarily. But if the gazelle initially moves away tantalisingly slowly instead of running away at once, at the same time jumping powerfully into the air with its legs held stiff (pronking), it is signalling: "Don’t even bother, I have plenty of strength to spare. Look for another victim!"
The graceful leaps of the gazelle find their equivalent in the disgusting spitting of the human male: a demonstration of surplus which makes the use of resources unnecessary, avoids risks and in the final analysis represents the antithesis to killing.

Spitting at an opponent can nonetheless symbolise male helplessness:
"I will never surrender, even if I am the last man.
Should I fall into the hands of the enemy, I pray for the strength to spit in his face."
Special Forces motto