Laertes is not a man used to losing.
There are those who think he’s letting Hamlet get those first two points. They think maybe it’s a way to get that poison Claudius has into him. But I really don’t think Laertes wants to let Claudius kill Hamlet – not because he doesn’t want Hamlet dead, he does – but because he wants to do it himself. I think Laertes is losing because he is distracted by his own ulterior motives, and the complex situation and also by his need to win. I think he is genuinely surprised to be losing here. I think he has to concede the point but he really doesn’t want to. And it’s probably fuel for the fire that leads him to jump out of line a bit and let the formality of the game go out the window. He’s losing. The only way to get his sword into Hamlet is to go a little loose cannon and attack.
Of course it could be played other ways. But this way makes the most sense to me and certainly has the most layers.