Playing Split Croquet Strokes Without Pull
by Pete Trimmer When playing a croquet stroke, the direction of the croqueted ball is usually ‘pulled’ (from how they were lined‐up) slightly toward the direction of the striker’s ball. Despite having played A‐class AC for over 30 years, it only recently occurred to me that it’s possible to play a split croquet stroke without any pull. The amount of pull depends on many factors (the angle of split, amount of roll, type of balls, milling orientation, temperature, and so on). Most player’s beliefs about pull seem to be based on trying things out and finding what works, rather than really understanding what is going on. Here, I take a somewhat unusual route into the subject, by starting with the more complex topic of cannons. This may seem a strange choice, but bear with me!
Figure 1a shows a 3‐ball cannon, with the balls in a perfectly straight line (pointing due north) … on a perfectly flat lawn. If the striker’s ball (blue) is then struck with the mallet toward the north east (diagonally up and right on the page), which direction will the most northerly ball (black) travel? Think it through before reading on. Given that the black is bound to travel generally northward, there are 3 possibilities: perfectly north (dead straight), north and slightly east (right a bit), or north and slightly west (left a bit).
I asked numerous players this question at the British Opens this year, and was somewhat surprised to receive all 3 answers. However, the vast majority of players answered that the black would travel very slightly in the direction of the mallet strike – slightly east of due north in this case. That was also the reply of a 6 time world champion, so you are in good company if that was your answer. The truth – a surprise to many – is that the ball will travel north and slightly west; the opposite lateral movement to the ‘normal’ pull of a croquet stroke. Many relative experts reading this may initially doubt my assertion. “Surely,” they reason, “the strikers ball pulls red slightly east of due north, so red must then also pull black a little east!?” I previously believed that logic, until I tried it numerous times (and in both directions, in case of a hill). As blue is struck north‐east, it imparts an anti‐clockwise spin on red, along with the northward impulse. That anticlockwise spin is then converted to a clockwise spin on black (again along with a northward impulse force). (Think of them as cogs, if that helps.) As the black starts to move northward, the clockwise spin becomes angled (the front of the ball spinning toward the east) and drives the black somewhat west. (Note that this is the opposite effect of an aerofoil effect – if the ball were just spinning in air, it would move the other way! Here, we’re talking about the effect of the spin getting carried into driving it along the grass.) The northward side of the ball (moving right due to rotation in the vertical axis) starts to move down toward the grass, so the clockwise vertical rotation gets converted into driving the ball west somewhat. Having understood that, we can use the same logic to think about a simple croquet stroke: without black being involved, the blue puts anticlockwise spin on the red, so as it travels north, the ball gets driven somewhat east; this is the essence of how pull occurs. Now consider Figure 1b: the blue has been moved 45° around red. Now, blue is being struck directly into red, so doesn’t invoke spin on red initially. Thus, the effect on black is to be pulled somewhat east of due north. This means that there is a position for blue, somewhere between the positions of Figs 1a and 1b, where the ‘spin effect’ (of
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