Every putt is a straight putt.
Every putt starts off straight. However, a breaking putt starts as a straight line before gravity forces the ball in a parabolic curve down the slope.
This statement seems as incredulous as the assertion by The Flat Earth Society that the world is flat. To the golfer, putter in hand, with a green shaped like an upturn saucer the putt looks anything but straight.
The fact is that very few putts are straight for their entire length. This is because greens are designed to allow water to run off rather that gather in pools on the surface.
Only putts straight up the slope (fall line) or straight down the slope are straight – all the rest have some break to them.
It is far more accurate to make the statement that every putt starts off straight before the slope of the green influences its roll.
How far the ball actually rolls in a straight line before it starts to deviate from its initial course depends on its out-of-the-blocks speed, the extent of the slope, and the height of grass over which it has to travel.
On contact with the putterface the ball lifts momentarily off the ground with backspin, contacts the surface and skids, and then begins rolling with pure forward rotation after about 15 inches according to the experts.
However, a more useful way of looking at a putt is to consider the three hypothetical phases that make up its path to the hole.
The duration of each phase depends on force of the initial stroke, the speed of the green, and the amount and direction of slope over which the ball has to travel.
For example, the acceleration phase of an uphill putt will be longer than that of a downhill putt of the same length as you have to stroke the ball more firmly.
From the point of view of the statement that every putt is a straight putt, the straight segment of breaking putts occurs in the acceleration phase when the ball is travelling too fast for it to be greatly influenced by surface friction and the force of gravity.
It is during the second phase, and particularly the third phase as the ball slows, that the break in the putt is most evident.
Television viewers of the US PGA Tour will be familiar with the aimline (target line) graphic.
It shows the relationship between the blue (now red) curved path to the hole and a straight line aimpoint to the side of the hole.
Because speed is a factor in assessing any break, the software that produces the graphic anticipates a terminal speed that would see a missed putt go by the hole by 16 inches.
If you trace a breaking putt from the hole back to the ball - the best way to read a putt - the path will pass through the apex of the break gradually straightening out until it reaches the ball in a final straight line.
Your aimline will be just wide of the apex. This is the straight line that gives rise to the statement that every putt is a straight putt.
1 = Illustration: Become A Putting Machine by Yvon Legault 2004
2 = Aimpoint Technologies