Your cat is imitating hunting behavior. This doesn’t mean that they want to hurt you, it is just that hunting for prey comes naturally to them.
Your cat is irritated. Since they can’t verbally vocalize what they like or don’t like, cats will show it in their own natural way, which is sometimes through cat bites.
Your cat is hurting. If your cat suddenly grabs and bites you without any obvious reason, and you are wondering why? Check for possible injuries your cat might have that you didn't notice.
Your cat wants to play. One of the most common times you may experience cat grabs and bites is during playtime, especially if you let your cat play with your hand when it was a kitten.
Overstimulation. Overstimulation or petting aggression is one of the most common reasons why your cat grabs and bites your hand. Cuddles are great but you need to know when to stop.
You accidentally hurt your cat. You might not realize you have hurt your cat, but it may react by pouncing or clawing to show you that something is not right.
Your cat might experience a burst of energy. It may cause your cat to go running and jumping around. It is not unusual to find that your cat grabs your hand, leg, or foot and bites you.
Your cat doesn't want you to stop. Cats usually like to have their own way. If you stop petting your cat, and it grabs your hand, it may be because it enjoyed it and wants more.