cl_nomeleehittime 2 (I think that's what it is)
Well, once you have hit someone, and once they recover.. there is a 2 second period that prevents you frrom hitting them. So don't make the mistake of flying up to them while they are recovering, because it's just going to be you that ends up getting hit.
Now, when you knock someone down, you can hit them multiple times, while they are rolling or still trying to recover from a hit. You have to be quick though, in order to perform these combos. You need to know your ESF to be able to do this. In time, you'll get the hang of things and pretty much know when to do what automatically.
For now, all you need to worry about is getting your opponent (Bot) at a disadvantage. Usually if you rush a bot, they wont be able to get you. You just need to know your timings well.