As with all game areas we start with the effect we are trying to create on the ball as it helps focus any strategies of set-up, mechanics or putter specs, for example.
The first aspect about the task of putting it to recognise that the weight of the ball on grass causes it to sit in a small depression. The longer and/or lusher the grass (on slow greens), the deeper the depression and vica versa.
As a result a good putt needs to go through three stages:
Launch - to get out of the depression
Skid - the ball is in contact with the grass but not rolling yet
Roll - where the ball is in constant contact with the green, rolling end over end.
Launch phase
If the ball launches higher than 3 degrees relative to the surface, it will leave the ground completely and bounce before rolling. If the ball launches lower than 1 deg it will hit the the edge of the depression and also bounce before rolling. In both cases, the point at which true roll occurs, is late and unpredictable, making distance control harder. The goal is thus 1-2 degree upward launch on fast to medium greens respectively.
The video below shows the effects of different launches in lab conditions.
Skid phase
Minimal skid is ideal. On a well struck putt, there should be less than 10 percent skid for the total distance the ball travels. So on an 8-foot putt, ideally there should be less than 10 inches of skid (see mage). Once “zero skid” occurs, the ball starts rolling on top of the grass smoothly.
When there is too much skid, the result is a loss of ball speed and thus distance. Every time the ball bounces and strikes the putting surface it loses energy — energy that has been factored into your putt for speed and distance. These putts tend to come up short and offline, and this often happens with long putts or lag putts.
Every putt, at some point, reaches zero skid and starts rolling. Reducing the amount of time it takes for the ball to reach zero skid will ensure that the ball will lose minimal energy and carry more momentum to the hole.
Backspin vs topspin
If a putt starts with backspin it will lose speed and can deflect offline more easily. However, the right amount of topspin will give you better distance control with your putts.. Why? Because the ball will lose less energy and stay on its intended line longer with spike marks or other imperfections on the surface.
Whilst the lesser of two evils, excessive attempts to create topspin (over 100 rpm at impact) could create more momentum and roll out than you want, making slippery downhill putts a smidge harder.
See the video below for the effect of different kinds of spin.
Roll phase
True roll is when the ball is in constant contact with the green. The goal is for this to start as early as possible, and to minimise the skid phase mentioned before, as true roll will mean the ball is less prone to being knocked off line by imperfections in the green.