According to the official rules of tennis, a player is not allowed to touch the net, the net posts, or the opponent's side of the court while the ball is still in play. Touching the net during a point is considered a violation, and it results in the loss of the point.
The relevant rule is covered under the "Code of Conduct" section (specifically, the "Unsportsmanlike Conduct" section) in the ITF (International Tennis Federation) Rules of Tennis. It states:
"Players shall not touch the net, net posts, cord or metal cable while the ball is in play."
The rationale behind this rule is to ensure fair play and prevent any interference with the natural flow of the game. Players are required to respect the boundaries and not make contact with any part of the net structure that could potentially affect the play.
There is one exception to this rule: if the ball bounces back over the net to the side where a player is located, they are allowed to reach over the net and play the ball without touching the net or net posts. In such a case, it is not considered a violation because the ball is now on the player's side of the court, and they have the right to play it.
Overall, players must exercise caution not to touch the net or its surroundings during a point to avoid committing a violation and losing the point.