Could you supply a little more detail? What are you wanting to say? The grammar is fine, but what is the meaning you want to convey?

The two parts of your sentence 'When I'm ready' and 'who can beat me' are correct, but it isn't clear what you are trying to say. The first part belongs in a sentence such as 'When I'm ready, I'll come and meet you.' The second is a question: 'Who can beat me?'. When you put the first and the second part together, they don't really mean very much.

When you are ready, your own pent-up frustration can beat you up.