Spin Rate
How fast the ball spins backward in flight, measured in RPM - it controls carry, stopping power, and how much a mishit curves.
Spin rate is how fast the ball rotates backward as it flies, measured in revolutions per minute. It is one of the three numbers - alongside ball speed and launch angle - that determine how far and how a shot flies. Spin creates the lift that keeps the ball in the air and the stopping power that holds greens.
Different clubs want different spin. A driver wants relatively low spin (roughly 2,000–3,000 rpm for many players) so the ball carries and runs rather than ballooning. Irons and especially wedges want high spin so shots climb steeply and stop quickly on the green. Too much driver spin costs distance; too little iron spin costs control.
Spin is heavily influenced by equipment: loft, the clubhead's center of gravity, the shaft, and the golf ball all move it. A higher-spinning ball or a wedge with fresh, sharp grooves spins more; a low-spin driver head or a firmer ball spins less. This is why ball fitting and club fitting go hand in hand.
Spin is also where mishits show up. Excess spin exaggerates curve, turning a small slice into a big one. Dialing spin to the right window for each club is a core goal of any fitting.