Since a curveball has topspin, that means the air behind it gets deflected upwards.

弧线球具有上旋球， 这意味着它后面空气会向上偏转。

However, it has a high topspin, and it's awkward to return.

但是它上旋球较，回球比较困难。

Man wouldn't know topspin if it hit him in the ball sack.

被击中下身才会知道上旋球厉害。

That's because the topspin on the ball forces it to drop sharply right before it reaches the opponent.

这是因为球上旋迫使它在到达对手之前急剧下降。

That's where power and topspin come in.

这就是力量和上旋进入地方。

So, Serena could be about to deliver a topspin serve, a power serve, or even a slice serve.

因此，小威可能会发出上旋发球、强力发球，甚至是切球发球。

Think of Nadal's swing; everything he does is to impart strong topspin on the ball.

想想纳达尔挥杆;他所做一切都是为了在球上赋予强大上旋球。

Understand the importance of topspin and using lobs to get the ball over the net at a higher trajectory.

了解上旋球和使用吊球以更迹将球越过网重要性。

It created a string bed that generated so much topspin that it was quickly banned by the International Tennis Federation.

它创造了一个产生如此多上旋球弦床，以至它很快被国际网球联合会禁止。

That's why Serena also uses topspin to her advantage, usually when her first power serve goes out of bounds.

这就是为什么小威也会利用上旋球来发挥自己优势，通常是在她第一次强力发球出界时。

But topspin serves are more accurate and still difficult to return.

但上旋发球更准确，而且仍然很难回击。

Because you see, the open stance shot doesn't have that topspin, and in an actual match, it can save two seconds.

因为你看， 开放站姿击球没有那个上旋球，在实际比赛中， 它可以节省两秒钟。

For example, Serena's average topspin serve is about 145 kilometers per hour, 25 kilometers per hour slower than her power serve.

例如，小威平均上旋发球速度约为每小时145公里，比她强力发球慢每小时25公里。

As long as you follow the eight-step practice method we mentioned last time, can control the ball, play some gentle rallies with others, understand what a topspin stroke is, and can turn your shoulder, that's a 2.5 level forehand.

只要按照我们上次提到八步练法，能控球， 能跟别人打一些温和拉球，明白什么是上旋球，能转肩， 那就是 2.5 级正手。

As long as you follow the eight-step practice method we mentioned last time, and can control the ball, play some gentle rallies with others, understand what a topspin stroke is, and can turn your shoulder, that's a 2.5 level forehand.

只要按照我们上次提到八步练法，并且会控球， 跟别人打一些温和拉球，明白什么是上旋球，能转肩， 那就是 2.5 级正手。