Spin without height is just a slower flat ball

Topspin only buys safety if the ball is hit high over the net, which is the part club players quietly skip.

Every coach in the world says hit with more spin for margin. The instruction is incomplete and the incompleteness ruins it, because spin on its own does not create margin. Height over the net creates margin. Spin is what lets you use the height without the ball flying long.

Watch a player who has been told to add topspin and has added it without changing anything else. The ball leaves the strings with plenty of rotation, passes about thirty centimetres over the net, and lands two thirds of the way to the baseline. It is safer than a flat ball only in the sense that it is slower. It gives the opponent a shorter, lower, more comfortable ball to attack, and it costs the hitter racket head speed. That is a worse shot in every respect except the one being measured.

The version that works looks almost wrong the first time you try it. A metre or more over the net, sometimes considerably more, with the ball landing deep and kicking up. That combination is genuinely difficult to attack and it is genuinely safe, because the error margin over the net is large and the spin is doing the work of bringing it down. The two properties only function together.

There is a reason players resist it, and it is not stubbornness. A high heavy ball feels defensive while you are hitting it. The satisfying sound and the sensation of flattening a ball out are strong reinforcers, and they arrive immediately, whereas the benefit of a heavy deep ball arrives two shots later in the form of a short reply you get to attack. Immediate feedback beats delayed feedback in learning, every time, which is why the wrong habit sticks.

I would put a rope above the net in practice and refuse to let anyone go under it for twenty minutes. It is an old drill, it is not fashionable, and it fixes more forehands than any amount of grip discussion.

The other thing it exposes is who is actually generating spin from the legs and who is doing it with the arm alone. Under a rope, the arm only players run out of ball speed within a few minutes.

Spin is not a quality of a shot. It is half of a trade, and the other half is height.