I think you might be on to something with naming the particular action. Stop is a good, clear instruction. I'd definitely give that a go. We had a phase of this, and it's one thing I'm pretty hard line on. Before going somewhere with other children, I talk to her about how she needs to be gentle, how to deal with it if she's cross etc. If she then hurts anyone deliberately, I see if she wants to apologise, and I do too, then we leave straight away. I know that sounds a bit extreme, but it does seem to work. Generally, Alice's response goes one of two ways. She either screams and cries to go back, in which case I'm sympathetic, give lots of cuddles and so on, but explain why we had to leave. At other times, she seems delighted to go, which gives me a clue about why she behaved like that, then we can talk about other ways to tell me she's unhappy. I know that's not always a practical option for everyone, but it's been a very effective solution for us.
Hope the phase passes quickly!