Observe. Under what conditions do the child's feelings overtake her? Is it when Mommy has been at a meeting the night before? After Mommy and Daddy have had an argument? During her little sister's time to nurse? When other children are crowding close to her? When playing with just one child? After being left to play with a sibling for 3 minutes? 5 minutes? 10 minutes? When wrestling and cuddling with Daddy or Mommy? Generally, you can come up with a good guess as to when your child might go "off track" and try to hurt.
Get someone to listen to you. In order to help your child, you need to reach for her--she's far away. Your heart will need to be warm. But our children's aggression kicks up lots of feelings--fears, angers, guilt--that freeze our warmth and make us likely to react in ways that frighten our child further. So find an understanding person who can listen to you talk at some length about how you feel about your child. Talk, and let your feelings show, until you can find your sense of caring and hope that things can get better. It's good common sense to clear our own emotional decks before trying to help with anyone else's emotional clutter.
Give up the hope that "this time it might not happen." Mental preparation is important. If your child often bites you when you're doing rough and tumble play, then every time you play this way, expect biting to come up!
When the situation is ripe for an aggressive act, get close, and offer warmth and attention. Your child needs you close by to help her tackle her store of upset.
Intervene quickly and calmly to prevent her hand from landing in someone's hair, or her teeth from fastening onto you, or her fist from landing on her friend. Because she's not in control of her behavior, she needs you to keep her from hurting someone. You can say something like, "I can't let you hurt Jamal," or, "Oh, no, I don't think I want those teeth any closer," while holding her forehead a few inches above your shoulder.
Reach for her with eye contact, a warm voice, and physical contact. She is far away, trapped in a knot of feelings, and she needs some sign that it's safe to show you what those feelings are. It's better not to move her away, or to get busy talking to her. The busier you are "fixing" the scene, the less safety she can feel. You can say things like, "I know you don't feel good," "I'm right here and I'll keep things safe for you," "Something's not right. Can you tell me about it?" "No one's mad at you. Can you look over here to see that I love you?"
Don't expect your child to be reasonable. She is feeling badly, you're telling her it's OK to feel, so she probably won't explain anything or use words to tell you how she feels. It's a mistake to expect children to verbalize their feelings while they're releasing them. Just let her writhe with upset, cry, and struggle. If she tries to hurt you, gently keep yourself safe by parrying her blows or using gentle restraint. Keep trying to let her know you care about her. The combination of you keeping things safe and you caring will let her cry long and hard about how awful she feels. When she's finished, she will feel reasonable, close to you, and relaxed.
Don't lecture or explain. Children know right from wrong. And they can't process your logic while they are wild with feelings. When they've blasted the feelings away, their own inner logic will be operating again, and they won't need you to tell them that you don't hit babies, or that biting hurts. Hitting or hurting will be the farthest thing from their minds.

