What does it mean to knock up in tennis?

Answer 1

knock up Verb

1. Also: (knock together) Informal to make or assemble quickly: my boyfriend can knock up a wonderful lasagne

2. Brit informal to waken: to knock someone up early

3. Slang to make pregnant

4. to practise before a game of tennis, squash, or Badminton

Noun

knock-up

a practice session at tennis, squash, or badminton

Answer 2

Its before the match starts 'for real'. Players 'knocking' the ball back to each other for warm-up / practice.

Answer 3

A warm up or short training session.