Sometimes parents need extra help with managing their child's oppositional behavior. A family therapist can help you and your child discuss problems and find ways to solve them. The therapist can also give you new techniques to manage behavior and give you a chance to practice them.
Make sure you choose a therapist with experience conducting therapy with oppositional youth. Child and adolescent therapists sometimes have this experience. Licensed Marriage and Family Therapist (MFTs) and social workers sometimes do family therapy also.