I would absolutely approach the perpetrator and have words and wouldn't hesitate screaming to bring attention to the behaviour or cruelty taking place.
I would also immediately call the police and take a photo of the person / car / anything that may prove identification.
I was actually in the situation where a homeless guy (who wasn't all together there) tried kicking my dog while we were out walking (we were totally minding our own business). I quickly picked my dog up fortunately the he didn't suffer the full brunt of the kick. Unfortunately, I didn't have my phone with me (of all times) but I started yelling at the top of my voice and asking people for help. The guy ran away but people around me were fantastic in helping me try to find him, including a convenience store owner who took myself and my dog into his shop and offered us water etc ... I reported the matter to the police, and although they couldn't do much, they were able to recognise the guy from my description (he had very specific shoes) for someone was homeless.
As it turned out he was known to police.
Subsequently I take my phone with me on all walks !