Tally up all the Grand Slam championships
won by current WTA players,
and you'll notice that nearly half
belong to just one person:
Serena Williams.
In fact, Serena is one of the most successful
tennis players of all time.
And that's in large part thanks to her iconic serve.
You can break Serena's serve into four parts.
The acceptance window is the area of the court
where the ball has to land in order for the serve to count.
It's determined by the minimum angle
for the ball to clear the net
and the maximum angle for it to land inbounds.
So, you can see here that the height
at which you hit the ball makes a big difference.
Chang Kee Jung: As taller you are, you have
more acceptance window.
Imagine Yao Ming learns to play tennis,
and if he hits the serve,
he will have a huge acceptance window.
Narrator: Serena isn't nearly as tall as Yao,
and she's not even among the tallest
female tennis players out there.
But she makes up for it.
Chang: So, Serena Williams does exceptionally well.
At the position when she hits,
her arms are fully stretched
and then she has a little bit of jump.
Narrator: The stretch and jump boost the height
at which she hits the ball,
increasing her acceptance window
and ultimately improving her chances
of hitting it inbounds.
Now, Serena isn't the only player who extends on the serve.
But, according to experts, she is much more consistent.
And it pays off.
Over the last 10 years,
she's won 82% of the games that she served.
That's a whopping 11% higher
than the average of the top 20 female players
over the same time frame.
But, of course, serving the ball inbounds
is just the first step.
What gets her all of those wins
is the fact that she makes her serves
extremely difficult to return.
That's where power and topspin come in.
Serena's power serve is one of the fastest in the game,
averaging 170 kilometers per hour.
That's about 12 kilometers per hour faster
than the average female professional tennis player.
Now, part of that speed is the result of pure strength.
Chang: Serena Williams, you can just see
she has, like, incredible, lean, muscular body,
so she can generate a huge amount of force.
Narrator: But what really sets Serena's power serve apart
is her timing.
To maximize power on the serve,
tennis players will bend their knees,
rotate and drop the hip,
lower the shoulder,
and, most importantly, twist at the trunk.
In other words, they use their whole body
to gain as much velocity behind the serve as possible.
But none of that matters if you don't hit the ball
at the exact moment when your arm is at full reach
and your body's in mid-swing.
In tennis, this is called fluidity.
And Serena is often credited
with the most fluid serve in the sport.
Chang: There will be no jerky motions.
You will smoothly hit the ball with maximum power.
Narrator: But there's a catch to these power serves.
Yes, they're fast, but the velocity
narrows the acceptance window,
making them less reliable.
That's why Serena also uses topspin to her advantage,
usually when her first power serve goes out of bounds.
Now, topspin serves are slower.
For example, Serena's average topspin serve
is about 145 kilometers per hour,
25 kilometers per hour slower than her power serve.
But topspin serves are more accurate
and still difficult to return.
That's because the topspin on the ball
forces it to drop sharply
right before it reaches the opponent.
That change in movement is thanks to a phenomenon
called the Magnus effect.
As the ball spins through the air,
it creates a pocket of lower pressure underneath it.
And it's that low pressure
that makes the ball drop abnormally fast,
catching many opponents off guard.
But Serena's second serve is not the fastest in the game.
Maria Sharapova, for example,
will fire her second serve at about 150 kilometers per hour.
But Sharapova sacrifices accuracy for speed here.
For comparison, Serena has scored, on average,
2 1/2 fewer double faults per match
than Sharapova over the last 10 years.
Chang: So, she combines the first serve,
of high speed, which is a little bit more risky,
but her second serve is safer.
However, it has a high topspin, and it's awkward to return.
And combining these two, she becomes excellent,
excellent service player.
Narrator: Meaning she scores more aces on average.
An ace is a successful serve
that the opponent's racket cannot reach
and therefore doesn't return.
Over the last 10 years,
Serena has recorded four more aces per match
than the average top 20 WTA players.
Last, but not least,
is the coup de grâce of Serena's serve:
disguise.
Chang: Another exceptional quality
is her ability to serve the ball
without telling the opponent
what kind of serve she will make.
Narrator: Check out this ball toss.
Normally, the way a player tosses the ball
will give their opponent a clue as to what serve is coming.
But not Serena.
She tosses the ball to the same spot,
with the same body position,
every single time.
Her toss is so consistent and smooth
that she manages something most others
find impossible to replicate.
She can disguise the serve.
So, Serena could be about to deliver a topspin serve,
a power serve, or even a slice serve.
Yet the opponent has no way of knowing what's coming.
Chang: These things are all disguised
until the very last moment.
And that makes Serena Williams'
serve exceptionally difficult to return.
So, for as long as Serena is competing,
these three words have the power to strike fear
into many pro players' hearts: