I gave a really long talk about service deception a few weeks ago to a teammate of mine in college.
There are a lot of factors that go into service deception, so I'll talk about them one by one as I remember them.
This is a lot easier if I made a video of this to demonstrate, but whatever; it's too late at night.
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Making all of your serves look the same. Now this is obvious, but this is easier said than done. Everyone will say this, but not many will give detail as to how to make thhe serves look the same. The below tips will help you out.
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Serving by contacting near the bottom of the ball (for short serves). The reason for this is, if you contact near the back of the ball, it is easier for your opponent to see what direction your paddle is moving in, thusing making it easier to read the spin. However, if your paddle is relatively flat, it is much harder for your opponent (who is 9 feet away) to see how much forward your paddle went.
With a flat paddle, it is hard to tell if you went to the side and a little forward, or if you went to the side and more forward.
Not only that, with a flat paddle, it is hard to tell if you went forward quickly, or if you went forward a bit slower.
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Serving the ball at the same speed, length, and height. This is related to having a flat paddle. Making short serves all look the same is a lot easier with a flat paddle, since you are kind of slowing the ball down (in a way, you are hitting the ball tangentially, since you are forcing the ball forward)
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Showing paddle at the last second (Hiding your swing). If your opponent can see the backswing of your serve, it can easily give away what direction your paddle is going in, thus letting the opponent read the serve more easily. This is easily done by having your paddle close to your body, and contacting it close to your body.
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Using mostly your wrist to vary the spin. This is related to backswing. The smaller the backswing, the harder it is for your opponent to read and react.
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Using a fast wrist. If your paddle is moving slowly, it becomes easier to read.
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Height of the ball toss is another varying factor. A high toss can change a service that normally would have been side-underspin, into just sidespin, due to how fast the ball is falling.
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Contacting the point at the same height. Now this one is a little more subtle. Usually when players serve some kind of no-spin/sidespin/side-topspin, they contact the ball at a fairly low point. To keep it consistent, you should be able to serve underspin also at a fairly low point.
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Optional tip: Have your paddle keep going down after you serve. Now, when you serve, most of the time, your paddle is going downward to carry the ball down. This is very noticeable when you serve any kind of underspin. Now, if you want your other serves to look the same, your no-spin, sidespin, side-topspin variations should all do the same.
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Optional tip: Have your paddle go from close to open (or open to close) for all similar looking serves. For example, if you do different pendulum serves, try having them all go from close to open. The reason for this is, it is a lot easier to serve no-spin/side-topspin serves with a more open racket, so it is nice if your service movement can disguise both.
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Optional tip: extra movement. Just a distraction
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Important Optional tip: Starting and ending with the serve the same way: Pretty obvious, but often the lack of this gives away the serve. There are so many times where I immediately can tell when someone is going to serve long simply from their body language.
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Optional tip: stomp when you serve. It can be a distraction, and you can play mind games (make your opponents pavlovian dogs), but one actual purpose of the stomp is to hide the sound of your service contact. Spinning the ball, and not spinning the ball: they make two different sounds, so if you can cover that up, great.
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TIP: On your computer on YouTube, you can pause the video, and look frame-by-frame by pressing the comma and period buttons. (I suppose it's really the < > buttons)
Look at first two serves that Fang Bo does in this video. He pretty much does most of the tips mentioned.
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In this video, observe how these players serve no-spin to each other. Think about what they did to make their serves spinny or not-spinny.
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Start at 1:10 to look at the serves. Pay attention to some of the things they are doing. Frame-by-frame.
Where did their paddles start from?
Where do their paddles go after contact?
Open to close? Close to open?
What direction is their paddle going in?
What direction do their wrist move in?
What direction is their forearm moving in?
What direction does their paddle face?
What direction does their racket head point to?
Think about these things when you watch these videos.
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There are some more tips that are more mechanically specific:
Changing where on the paddle you contact the ball is a pretty good way of changing how fast your racket hits the ball, varying the amounts of spin you put on the serve.
For example, contacting near the handle on a wristy serve should give less spin. This is pretty good for serving no-spin.
There are others, like doing things that are different from what's usual, like:
(This one is hard to explain) Changing the direction you move your wrist, but keeping the same appearance. This one is easier to explain with pictures, so:
This is related to having your wrist and your forearm go in slightly different directions (which is another thing you can do).
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