Guidance to Referees and Players on 13(a)6 and 8
Appendix B of the 4th Edition Rules booklet gives some clear guidance on faults related to hitting balls along their line of centres when close together. This can be used by referees to decide faults in a range of typical situations, and is soundly based on the super slow-motion videos made by the CA in 2006.
Some queries have been raised concerning what decisions could/should be made when the stroke is played at an angle to the line of centres.
There is a range of angled strokes - not as common as straight clearances but nonetheless important - which is difficult to referee - the following gives guidance. Bill Arliss's latest DVD [The practical side of GC Refereeing] covers this in some detail including some new video analysis. The following guidance is distilled from chapter 5 of this DVD.
Guidance to Referees and Players
Where the striker's ball (SB) is driven straight at the object ball (OB), Appendix B gives guidance as to what situations will give rise to a fault, and how to detect them.
In cases where the line of aim is at an angle to the line of centres of the balls, the following guidance can be given.
Refer to the diagram and note the following abbreviations used:
- Aiming Angle to line of ball centres (AA) in degrees
- Initial Separation (IS) of the balls in millimetres
- Departure Angle (DA) - the angle in degrees at which the balls separate after impact
The following guidance assumes well-executed stop shots. Note always that poorly played strokes with excessive or lazy follow-through will be likely to cause a fault even in circumstances when a well-executed stop shot would not - this must be taken into account when refereeing a stroke.
Video evidence has confirmed that a Double Tap 'Ball Crush' will generally reduce the DA of the two balls after contact. In a clean stroke, the DA is something between 65 and 90 degrees; in a fault, the DA will be less than 60 degrees - it is this fact which can be used to decide the fairness of strokes.
There are many potential situations, which have been generalised into these three groups to aid players and referees:
- Straight or nearly straight strokes:
If AA is < 10, treat the stroke as though it were straight and apply the guidance in Appendix B.
- Angled strokes with balls separated by at least 3mm and where both balls move more than 600mm:
If AA > 10, then if DA < 60 the stroke should be faulted under 13(a)(6) or (8).
- Gentle or very angled strokes with small initial separations:
- unless both balls move an appreciable distance, it is difficult to tell anything useful from DA. Instead, before the stroke is played, ask the player to indicate the intended line of aim and estimate how far the relevant point on the SB's perimeter will travel before it contacts the OB. If <4mm, the stroke should be faulted under 13(a)8.
- using the approach in 3.1, the smaller the IS, the larger the AA required to avoid a fault.
- With IS = 2mm, the stroke must be played with AA > 60 degrees to avoid a fault when played with a stop shot and AA > 70 when played with a full drive
- With IS = 1mm, the stroke must be played with AA > 75 degrees to avoid a fault.
When played correctly at such extreme angles, the OB will not move very far at all - if it moves a significant distance, then there is likely to have been a fault under 13(a)8.
How to Referee Such Strokes
- Ask the player what they intend to do. The referee needs to know:
- what is their intended line of aim and hence what AA they intend;
- the type of stroke that they intend to play (i.e. stop shot or drive); and
- how hard they intend to play the stroke.
- Check the separation between the balls along the line of centres. If the separation is <3mm, also check how far the relevant point on the SB's perimeter will travel parallel to the intended line of aim before it contacts the OB.
- Mark the initial positions of both SB and OB. Be ready to mark the departure directions of both balls. Ideally, ask the opponent to mark the line of the OB (because that is relatively insensitive and will not deviate very much from the initial line of centres) and an assistant to mark the line of the SB.
- Ask the player to play the stroke.
- Watch the stroke - was it along the intended AA, was it a well-executed stop shot? Consider the DA.
- Apply the guidance given to decide whether or not to declare a fault under Rule 13(a)(6) or (8).