The first 20% of a putt is not rolling at all
- Greens & ball roll
The ball you have just struck is not actually rolling. It hops, it skids, and only then does it start to roll.
This article goes through what happens in each of those three phases, then compares in numbers how long the sliding phase is and what changes it. At the end there is a summary of what it means for you as a player. All numbers come from the same physics model as the Putt Break Calculator.
The hop
A putter has 2–4° of loft, so the ball lifts very slightly off the surface. It is projectile motion, so the distance is:
d = v₀² sin(2β) / g
At a launch angle of 2° and an initial speed of 3 m/s that is about 6 cm. We are talking about centimetres — but while the ball is in the air there is no contact force, so seen from above it travels perfectly straight.
Here is a 6 m putt with only the launch angle changed:
| Launch angle | Airborne | Skid | Total straight section |
|---|---|---|---|
| 0° | 0 cm | 75 cm | 75 cm |
| 2° | 7 cm | 70 cm | 77 cm |
| 4° | 18 cm | 62 cm | 80 cm |
| 6° | 27 cm | 56 cm | 83 cm |
More loft makes the ball fly further, but it then skids less after landing, so the total straight section barely changes. What loft really does is lift the ball out of the small depression it sits in, so it starts out cleanly.
The skid
On landing the ball has almost no spin. The contact point slides, and sliding friction slows the ball down while spinning it up at the same time. The slip disappears and pure rolling begins at the moment the speed reaches:
v_roll / v_land = 1 − (2/7)(1 − r)
where r is the amount of topspin at launch. With no spin at all that is 5/7. This ratio is an exact result for a rigid sphere and does not depend on the sliding friction coefficient.
In other words, the ball loses close to 30% of its speed while it slides. To cover the same distance it has to start about 20% faster than a ball that rolled from the outset.
This is what the calculator's launch breakdown shows for a 6 m putt:
How long is the skid?
The length of the skid is set by the sliding friction coefficient and how fast the ball starts. Here it is by putt length under the site's standard conditions (Stimp 10):
| Putt length | Airborne | Skid | Straight section | Share of the putt |
|---|---|---|---|---|
| 1 m | 2 cm | 15 cm | 17 cm | 17% |
| 3 m | 4 cm | 38 cm | 41 cm | 14% |
| 6 m | 7 cm | 70 cm | 77 cm | 13% |
| 10 m | 11 cm | 113 cm | 124 cm | 12% |
On longer putts the skid itself is longer, but its share of the putt falls slightly. Putting researcher Dave Pelz reported this phase at 15–20% of the putt. Under the site's standard conditions it comes out at 12–17%, broadly the same range.
What changes the length?
Changing one condition at a time on a 6 m putt:
| Condition changed | Straight section | Share of the putt |
|---|---|---|
| Standard (Stimp 10, sliding friction 0.25, 20% topspin) | 77 cm | 13% |
| Slow green (Stimp 8) | 93 cm | 16% |
| Fast green (Stimp 12) | 65 cm | 11% |
| Slippery turf (sliding friction 0.15) | 117 cm | 20% |
| Grippy turf (sliding friction 0.4) | 51 cm | 9% |
| No topspin (0%) | 103 cm | 17% |
| Strong topspin (40%) | 54 cm | 9% |
The biggest effects come from how slippery the turf is and how much topspin the ball leaves with. On slow greens you hit harder, so the ball slides further; on fast greens the slide is shorter. "The first 20%" is the figure for slippery conditions — on an ordinary green, a little over 10% is a better guide.
Why a putt breaks late
You will sometimes read that a putt runs straight early on because sliding friction holds back any sideways movement during the skid. Work it through and that is not what happens.
A slope pushes a sliding ball sideways too. Sliding friction does resist sideways slip, but by the time the slip has gone the ball has picked up exactly the sideways speed it would have had if it had been rolling from the start (in both cases, 5/7 of the pull of gravity along the slope).
For a 6 m putt on a 2° side slope, the sideways deviation at 25% of the way was 4.7 cm in a model that ignores the skid, and 4.5 cm in one that includes it. Barely any difference.
The real reason a putt runs straight early on is that the ball is moving fast.
curvature = sideways acceleration / speed²
For the same sideways acceleration, twice the speed means a quarter of the curve. Because of the skid, the ball has to start about 20% faster to cover the same distance, and the early part of the putt is that much straighter.
The feeling that a putt "goes straight at first and breaks hard at the end" is backed up by the physics exactly as you would expect.
What it means on the course
- The first 10-odd percent of any putt runs straight, whatever the line — about 80 cm on a 6 m putt. Picking a spot 30–50 cm in front of the ball makes sense: you are setting the direction inside that straight section
- Read the break in the second half. Most of the curve happens near the hole, once the ball has slowed down. How to read it is covered in "Three things to look at first when reading a green"
- On slow greens, or with dew still on them, the slide is longer. You have to start the ball faster, and putts tend to feel as though they "don't roll out"
- What a "better roll" putter does is shorten the skid — by 20–30 cm on a 6 m putt. But you re-learn your distance control through practice anyway, so the effect on how many putts you hole is likely small (an inference from the numbers)
- Too much or too little loft leaves the total straight section almost unchanged. Choose loft for a clean launch (does the ball come out of its lie cleanly?)
This skid phase is part of what the Putt Break Calculator computes. Enter the side slope and the distance and you can see in 3D where the ball starts to turn. Change "Sliding friction μ" or "Topspin at launch" and you can try how the length of the skid shifts the break.
Conditions: the site's physics model. Stimp 10, 2° launch angle, 20% topspin at launch, sliding friction 0.25, 15% extra drag at low speed, no grain. Every putt is hit hard enough to finish 40 cm past the hole.