Except the ball is allowed to bounce twice.
The second bounce can be either inside or outside the court boundaries.
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This is one of the reasons wheelchair tennis has become so popular - people in a chair can easily play against able-bodied friends.
The quad division is slightly different in that it is for players affected by three or more limbs.
Wheelchair tennis really took off in 1976.
People in wheelchairs had played before.
But it was only when disabled American Brad Parks first hit a tennis ball that he realised the potential of this new sport.
Brad and his friend Jeff Minnenbraker went to great lengths to set up exhibition matches and get publicity.
It's popularity grew and in 1988 eight countries came together to form the International Wheelchair Tennis Federation.
The game also grew very quickly in Belgium.
That was because of Dutch teenager Chantal Vandierendonc.
Chantal played national level tennis but a car accident left her a paraplegic.
Prize money
When she discovered wheelchair tennis she realised she could play the game she loved again.
Her father Jules organised the first Dutch Open in 1985.
Today, the Dutch women are the best in the world with five out of the top six in the rankings coming from Holland.
There is a professional wheelchair tour where players such as Britain's Jayant Mistry compete in tournaments all over the world for prize money.
But the pinnacle of the sport is the Paralympic Games.
Wheelchair tennis was introduced in Barcelona in 1992 with the quad division making its first appearance in Athens in 2004.
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