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The CA Slow-Motion Videos - Stroke Guidance for Players and Referees

In September 2006, a CA project team of Bill & Pam Arliss, Barry Keen, Alan Pidcock and Ian Lines undertook some slomo (slow motion) videoing of series of types of stroke at Bowdon. The conclusions from analysing these videos have informed both how AC laws and GC rules have developed since, and how referees are now trained.

The videos themselves are now all hosted on YouTube; our thanks to Bob Kroeger for uploading the videos to YouTube. The following introduces each series, gives the YouTube link, then concludes with a summary of the learning from each series.

Reviewing these videos will help you be a better player or referee, by understanding what is, and is not, legally possible in a range of common strokes.

The Series

The series were:

  1. single ball shots
  2. double tap situations with two balls
  3. normal two ball croquet strokes
  4. hoop running starting from close to hoop
  5. hammer shots
  6. jump shots

…all are shown in both normal and high speed forms, so you can compare what you see with the "naked eye" with what slomo reveals.

The slomo videos were taken at up to 8,000 frames per second, compared to normal video which is shot at 24fps.

Series A - Single Ball Strokes


Half played as drives, half as if rolls. Not the most exciting series, though the main learning is that contact between mallet and ball ends within 5mm of the point of impact. So for example, striking a ball more than 5mm away from a hoop upright is not going to be a crush unless the ball checks on the upright and the mallet catches it up again.

Series B - Two Ball Double Tap Situations


These strokes are of particular interest in GC, where clearances on an opponent ball were often suspected of being double taps (DT). They can also occur in AC scatter shots - although when the object ball is being roqueted in the stroke, the player is exempted from an DT by law 28(d)1(A).

Following video analysis of these strokes, new rules/ laws were introduced for strokes where the balls start close together and either a DT or a "ball crush" (striker's ball crushed between mallet and the object ball) may occur. These are rule 13(a)8 in GC and law 28(a)8 in AC.

The conclusions for GC in straight clearance strokes are published as Appendix B of the 4th Edition Rules booklet and can be summarised as:

1. For more or less straight shots, if the starting separation is 4mm or less, a fault will have occurred.

2. For straight shots with larger separations (up to 50mm), a double tap will have occurred if the object ball travels less than 8 times the distance of the striker's ball. A fault may still occur above 50mm separation (and still be shown by the relative distances travelled) but becomes less likely.

For angled close clearance strokes the situation is quite complex, but guidance to players and referees has been published: Close Angled Clearances

Series C - Normal Croquet Strokes


In this series the following suffixes were used to describe the shot type.

  • D -drive
  • H - half roll
  • F - full roll
  • P - pass roll
  • S - stop shot

This series showed that many "normal" Association Croquet strokes involved either DTs or "maintenance of contact" between mallet and ball, when assessed using slow motion video. Consequently, AC law 28(a)7(A) was qualified with the word "visibly" to ensure normal croquet strokes would remain playable.

Series D - Close Angled Hoop Strokes


This series of videos were revelatory, as careful analysis of the slomo videos showed the majority of such strokes are in fact clean, even though they might once have been judged faults with a naked eye. The way GC referees were trained was changed as a result of these videos. The GC guidance to players and referees on close angled hoop strokes played firmly is:

If the ball exits the hoop at a reasonable speed (given how hard it was struck) and more or less straight (+/- 15 degrees from straight) or to the same side as it entered (like a "reflection" from the far upright), it will be given as "clean" unless some evident fault is observed. If it exits slowly and substantially on the opposite side to its entry, it will be declared a fault.

Series E - Hammer Strokes


This series examined hammer strokes, where the mallet is driven downwards at a steep angle onto the ball, usually in some hampered position.

A firmly-played hammer stroke will make the ball "rebound" from the lawn if played cleanly - if it doesn't, this is evidence the ball was trapped by repeated or prolonged contact with the mallet, as is a muffled contact sound. Slow-motion video evidence shows that hammer strokes played even at relatively gentle angles like 30 degrees to the horizontal are in fact often double taps, even though this is not obvious to the naked eye.

To foster consistent playing and refereeing standards, it will be normal practice to fault any firmly-played stroke where the mallet strikes the ball more steeply than at 45 degrees to the horizontal and which is not seen to rise from the surface as a result. A badly played hammer stroke at less than 45 degrees may also give rise to audible double taps and should be faulted accordingly.

The same faults might arise when hitting down on a ball in a hoop hampered by another ball close behind the striker's ball - however these are often played quite gently and so may not give rise to these particular faults. The referee should make a decision about such gentle strokes based on their
judgement of the particular stroke.

The CA has published guidance for players and referees of GC on hammer strokes.

Bob Kroeger has also published his own series of hammer stroke videos which supports these same conclusions: https://www.youtube.com/watch?v=jEc3HhhVupM

Series F - Jump Shots


These show no law or rule infringements.

The Full Report

In 2008, once the laws and rules had been revised to reflect the new knowledge which came for this video analysis, the report of the video project was updated accordingly: High Speed Filming report v3


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