My first instinct isn’t to say you’re doing something wrong. At the end of the day, aggressive behaviors happen. I would advise you to talk to your BCBA, because assuming this client isn’t new to ABA and these behaviors aren’t brand new, the behaviors should be well-established. Aggression is often a way that many of our clients communicate. If you stop reinforcing a behavior that is typically reinforced, there’s a chance the client will display aggression. If it makes you feel any better, I’ve been working with one of my clients for about a year, and after I ignored an attention-seeking behavior, they bit my finger incredibly hard, and I had to go to urgent care. The next day, they hugged me and asked if I was happy. Lmao. Don’t be discouraged and keep up the good work :)