My cat is almost always nice and calm, but sometimes his pupils delate, he stares at me intently, then raises on his back legs to reach my arms while I'm sitting in a chair and strikes me with his paw. The strike isn't particularly hard, but his claws are out. He's not being playful — if I try to take him in my hands, he squirms, scratches, bites. These periods of aggresion are very short and don't happen too often, but are annoying and worrying.
I've tried to turn this fight into play by throwing balls, and it almost works, but I'm afraid this will teach him that hitting me will result in playing, and I'd obviously like to avoid this.
My cat is neutered, I play with him often, so I don't understand why this happens. How to stop my cat from being aggressive?