When the tomcat grabs the female by the scruff of the neck when mating he is not being the macho male; he is defending himself by using an “immobilisation reaction behavioural trick”.
He knows that the female is the boss in sexual matters. She is dominant on these occasions. The female swipes and lashes out at the tomcat. He has to protect himself.
We know – because we see it so often – that male and female cats retain, throughout adulthood, a special response when grabbed firmly by the scruff of the neck which goes back to the days when they were kittens and their mother moved them around from den to den.
Kittens have an automatic reaction to being held in their mother’s teeth by the scruff of the neck. They have evolved a freeze reaction which means they become passive and don’t struggle which is essential when the mother is involved in the difficult task of looking for a safe place which may mean carrying a kitten over difficult terrain, up a tree or through dangerous passages. Adults don’t lose this response.
We know this because one of the techniques to pacify a cat is to hold him/her by the scruff of the neck. This should be done with a certain amount of sensitivity but it does work. Also, you will see on the Internet people (and I disagree with this quite strongly) placing a clothes-peg (clothespin) on the scruff of a cat’s neck whereupon the cat usually becomes passive and if the cat is a kitten they sometimes fall over as if paralysed, so dramatic is the reaction.
So returning to sexual matters between tomcat and female, the male engages in this immobilisation trick to keep the female passive and from stopping her being aggressive towards him. He temporarily transforms her into a kitten hanging from her mother’s jaws fastened around the scruff of her neck.
Unneutered stray, tomcats as, we know, can be engaged in vicious fights between themselves and they certainly do not wish to receive more scars from the female with whom they wish to mate.