26 August 2014

Cliff's question

Last Saturday, we were standing on the balcony in pleasant August sunshine with a beer in hand, watching Petersfield's pre-season warm-up match against a Chichester XV, refereed by the excellent Mike Gill.  In the third quarter, Petersfield scored a try close to the near touchline.  The kicker brought the ball back to the 10 metre line to gain the extra two points for the conversion. Cliff asked why they brought the kick so far back, and I agreed - it looked too far.  Indeed the kick missed.

 Obviously, the reason that the kicker brings the ball back from the try line is to make the apparent target as big as possible.  The parallax effect means that the goal posts look wider apart as you move back, but at the same time the distance for the kick grows, making the kicker's task more difficult. What's the ideal distance to bring the ball back?  Is there a simple way to work this out in the heat of the match?  Probably every professional kicking coach knows this, and maybe there are doctoral theses on the subject, but here's my take on the question. 

The geometry is simple - the width of the target depends on the distance back from the try line and the distance of the mark made by the referee from the mid-point of the goal posts.  The width of the target can be shown as the angle viewed by the kicker from the point where the ball is placed.  So assuming that the pitch has been marked up properly and is rectangular in shape, the following table shows this angle for various positions (distances in metres, angles in degrees):

Offset from
centre line
0 5 10 15 20 25 30 35
Distance from try line 10 31.3 25.5 16.2 10.0 6.5 4.5 3.2 2.4
15 21.1 19.1 14.8 10.8 7.8 5.7 4.3 3.3
20 15.9 15.0 12.8 10.3 8.0 6.3 5.0 4.0
25 12.8 12.3 11.0 9.4 7.8 6.4 5.3 4.3
30 10.7 10.4 9.6 8.6 7.4 6.3 5.4 4.5
35 9.1 9.0 8.5 7.7 6.9 6.1 5.3 4.6
40 8.0 7.9 7.5 7.0 6.4 5.8 5.1 4.5
45 7.1 7.0 6.8 6.4 6.0 5.4 4.9 4.4
50 6.4 6.3 6.2 5.9 5.5 5.1 4.7 4.3

The widest angle for each 5 metre distance (wide and back) is highlighted in the table.  With the crossbar at a height of 3 metres, I don't think many people will choose to kick from closer than 10.

So on this basis, it looks as though the widest angle is always given by taking the ball back as far out as the mark is from the centre of the posts.  On a full-sized pitch, this means that a line through the crossing point of the 15 metre dashed lines (20 metres from the centre of the pitch) and the 22 metre line is very close to the best apparent target.  And conversions from the touchline should never be further back than about 5 metres short of the 10 metre line.

The other important factor in deciding whether to kick, and where from, is the distance.  A kick taken too far back will need a huge knock.  Here's the distance table with the same squares highlighted as in the table above:

Offset from
centre line
0 5 10 15 20 25 30 35
Distance from try line 10 10.0 11.2 14.1 18.0 22.4 26.9 31.6 36.4
15 15.0 15.8 18.0 21.2 25.0 29.2 33.5 38.1
20 20.0 20.6 22.4 25.0 28.3 32.0 36.1 40.3
25 25.0 25.5 26.9 29.2 32.0 35.4 39.1 43.0
30 30.0 30.4 31.6 33.5 36.1 39.1 42.4 46.1
35 35.0 35.4 36.4 38.1 40.3 43.0 46.1 49.5
40 40.0 40.3 41.2 42.7 44.7 47.2 50.0 53.2
45 45.0 45.3 46.1 47.4 49.2 51.5 54.1 57.0
50 50.0 50.2 51.0 52.2 53.9 55.9 58.3 61.0

So you can see that a 10 metre error in the positioning of a touchline conversion will change a 49.5 metre kick to 57 metres, as well as making the angle worse.  On the other hand, taking the same kick from just outside the 22 metre line will worsen the angle by only 0.3 degrees (next to nothing) and make the kick 6.5 metres shorter - could be important for some kickers. 

All of these calculations assume that a kicker can hoof the ball 50-60 metres - easier at altitude - and they ignore weather conditions and pitch slopes that will lead to a more complex decision-making process.  But it does look as though many kickers are making their task more difficult.

Feedback welcome. 

25 July 2014

Sky Sports

At last I've done the deed.  I thought about it and blogged about it last year.  The final straw was another price rise and reduction in useful service, which has at last pushed me over the brink to cancel Sky Sports. 

Sky used to be the place to watch Aviva Premiership matches, and cycling through Eurosport.  The rot started when they started failing to provide proper coverage (semi finals on ESPN, for example).   Then they moved Eurosport out of the Sports packages into an Entertainment package, best described as a pile of infantile rubbish costing extra £5 a month.  Eurosport is sport, isn't it?  And then they lost the rights to show Aviva Premiership Rugby to BT, and put the price up at the same time, presumably to provide even more funding for football players to keep their WAGs in the accustomed style. 

In the 2013-14 season, the BT coverage started a little shakily but has gone from strength  to strength.  They have a great team of presenters, a fun format, and can bring a smile to your face in the midweek programme, unlike the tired old Sky show that we used to endure.  Sky Sports is characterised by people sitting around in suits, BT by people enjoying themselves.

Any Sky Rugby coverage that I need to watch is shown at our local pub or at Grayshott Social Club.  £20 a month or thereabouts is a high price to pay for the occasional Championship, Super Rugby or tour match.  What about other sports?  The BBC's  Formula One coverage isn't as good as Sky's, but it's acceptable.  Frankly Sky F1 is overblown, too many hours of blather; the noise to signal ratio is too high.  I rarely watch it live, and delete most of it without watching the recording.   Cricket isn't worth watching at the moment; Test Match Special on BBC Radio 4 LW is enough pain.  And I've said enough about wendyball already.  Better without it.