In tennis, the knock-up is the short time before the match really starts, when the two players hit the ball to each other to get warm and to feel the court. It does not count on the scoreboard.

In tennis在網球裡, the knock-upknock-up is是 the short time before the match really starts比賽真正開始前的一小段時間, when the two players hit the ball to each other雙方球員互相對打, to get warm讓身體熱開 and to feel the court並感受一下場地。It does not count它不算進 on the scoreboard計分板。

You will hear this from tennis people, especially in British English.

You will hear this你會聽到這個 from tennis people從打網球的人口中, especially尤其是 in British English在英式英文裡。

A knock-up lasts a few minutes: they try a few serves, they loosen their arms, they see how fast the ball is coming.

A knock-upknock-up lasts持續 a few minutes幾分鐘: they try a few serves他們試發幾個球, they loosen their arms活動一下手臂, they see how fast the ball is coming感受球飛過來的速度。

Though actually, the verb knock up means other things in other rooms of English — to make something quickly, to wake someone by knocking, and, in informal American English, to make a woman pregnant — so this tennis noun is a small, special use. Here it is only that warm-up hitting.

Though actually不過其實, the verb knock up動詞knock up means有別的意思 in other rooms of English在英文的其他場合裡——to make something quickly很快做出某樣東西、to wake someone by knocking敲門叫醒某人, and而且 in informal American English在美式口語裡 to make a woman pregnant指讓女生懷孕——so所以 this tennis noun網球裡這個名詞用法 is a small, special use算是一個小小的特殊用法。Here在這裡, it is only它只是指 that warm-up hitting那段熱身對打。