I would cut his claws so he can’t do as much damage when he scratches. An intact cat is much more aggressive than a neutered cat, especially if they smell a female in heat. My male cat was neutered at 6 months of age.
Another reason that cats might scratch is he might be in pain for some reason. If you pick up a cat or touch a spot that he is experiencing pain, it’s a natural instinct to protect himself and scratch. If a cat has stomach pain due to hairballs, or bladder pain due to infection, you may not know about it and touch him in these areas and he reacts.
If he is neutered and still gets aggressive I would take him to the Vet to see if there is anything wrong. If he is neutered and it was only done recently there will still be male hormones in his system and he still might react to a female cat in heat.