Well the side palm or jak jeung in Cantonese, is another very common Wing Chun technique. And it's unfortunately, it's always a bit confused with pak sau. Pak sau means slapping hand, and it's also a very common technique in Wing Chung. However, the side palm is normally used in a slightly different situation.
If somebody's standing in front of you, especially if they're just in a guard; maybe he gets too close to me, maybe he hasn't attacked me yet. Then normally, I will do a pak sau to come in, and kind of take care of him. But that's normally a preemptive movement, all right?
If he were to give me a strong punch with the elbow out, which is very typical on the street, that nobody is going to punch you on the street like a Wing Chun person. They are always going to punch you like this. Sometimes pak sau can be problematic, especially for people who are a little bit smaller and weaker. If he gives me a strong punch, and I try to do pak sau, a lot of people get caught on the arm where they're not able to go up and punch.
For that reason, we have the side palm, which is in the third set of the siu nim tau part. When he goes to fire a punch at me, I come underneath this way here, so I actually don't need to clear his arm out of the way to clear a space from my punch. I can let his punch ride by, and I hit him underneath with this one here.
After I've hit him, then of course I have all the options to come in and chain punch, and do whatever. But the side palm is nice, because it follows the center line theory. Because, if a punch is really high, all right, then the shortest line between me and my opponent is not to go up and over to punch him here. The shortest line is right here. So, that's why this makes a much more effective defense, especially for someone who's smaller, or weaker, to go in and punch underneath the guy's arm, rather than trying to climb over the top.
So, a side palm can be really useful. It can also be used, although it's a little bit risky, if he ends up punching with his back hand, and then he comes in here. I can use the side palm this way here, and punch him on the inside.
Now, any time you go on the inside, it's very risky because you always have to worry about the other hand coming in. But you don't always have a choice in fighting. Somebody attacks you really quick, and you have to react. Of course, we would prefer to always be on the outside which is much safer. We have a lot more options here. But it's not always your choice. Your opponent doesn't attack you in the way you want to.
So, a side palm can be done outside, can be done inside, and it's a great replacement for pak sau when you're a little bit late, or the guy has already launched the punch. You don't need to clear it, you can just slip it underneath.