Mark Taylor (@MarkTaylor0) writes the excellent 'Power
of Goals' blog.
Rugby Union, much like football is a fluid, fast moving sport,
which requires a large amount of context related data to adequately
describe on field events. However, rugby also has a
reasonably large array of discrete events, such as kicks at goal,
where the object of the play is well defined. The quality of
shooting chances in football can be calculated with reasonably
clarity by using such information as the x and y field coordinates
of the event and the same can be done using a logistic regression
approach for penalty and conversion attempts in rugby.
OptaPro have kindly supplied kicking data from a wide range of
rugby competitions from 2010 through to 2012, including English
domestic league matches, European and domestic cup games,
Internationals and Six Nations matches as well as domestic and Tri
Nations Southern Hemisphere contests. Some of the data also
included age restricted matches from the under 20's Six Nations and
the IRB under 20's World Championship.
A model for the expected success rate for kicks at goal can be
constructed using knowledge of the position, distance and angle
from where the attempt was taken, combined with the actual outcome.
We can then use this scoring expectation to not only rate the
records of individual kickers more accurately by accounting for the
relative difficulty of the kicks they attempted, but also chart the
career development of young players. We can also begin to
investigate the drop off in kicking effectiveness, both generally
and individually with increasing distance and this opens up the
development of in game strategies which may decide whether a side
decides to kick for goal or kicks for the corner.
Common sense tells us that increasing distance from goal and
increasingly widening of the kicking angle will make a kick less
likely to be successful. For example, a kick, twenty metres out and
in front of the posts, based on the data from 2010-2012 will be
successfully kicked about 95% of the time. However, move the ball
to the touchline, so that the ball is still twenty metres from the
tryline and the kick becomes much more difficult. A combination of
the angle and the increased actual distance to the posts now makes
the kick just a 60% chance to be converted by an average
I've initially included all players in the sample in setting a
baseline for kicking ability, so the group includes promising
youngsters, such as Owen Farrell, who played in the IRB under 20's
World Championship, as well as for the full England team during the
course of the data and also includes household names in the later
stages of their careers, such as Jonny Wilkinson and Andy
The analysis compares the expected success rates for kicking
attempts, comprising both penalties and conversions, based on the
field position for each kick. I've used an arbitrary cut off point
of a minimum of 75 attempts to qualify for inclusion in the final
list, because small sample sizes can often produce extreme outliers
which can make players appear either much better or much worse than
they actually are. Most Southern Hemisphere players are omitted
from this initial analysis.
Wales' Leigh Halfpenny tops this fleeting glimpse at recent
kicking ability. The data omitted the Celtic league clashes, so his
figures originate from International, World Cup and European games
and his number of attempts just exceeded 100. Judged on
kicking field position, an average expected return was 71 successes
from 107 kicks at goal and Wales' full back and now fulltime kicker
made 88, almost 25% higher than an average player from the dataset
would expect to achieve.
Halfpenny originally took just the long range kicks for club and
country and his total attempts have a much higher proportion of
kicks from extreme distance than most others on the list. Over 16%
of his kick attempts travelled 50 metres or more in the air and if
we further break down his actual success rate compared to
expectation, we see that he truly excels at these longer kicks. An
average player's expected success rate for Halfpenny's kicks of 40
metres or more would have been 24 successes from 49 attempts and
Wales' full back actually made an astonishing 38. Overall Halfpenny
is a slightly above average kicker at distances short of 40 metres,
but exceptional beyond that. The quality and range of his kicks
combine to make him the top kicker.
Halfpenny going for the posts
The inter-play between a kicker's range and his accuracy can
also be demonstrated by comparing two current Irish internationals.
O'Gara is nearing the end of his international career, while Sexton
is just beginning his. The numbers from the table above can help to
pinpoint their respective kicking strengths and weaknesses over the
last couple of seasons.
Proportionally Sexton attempts more kicks beyond 40 metres than
does O'Gara and in addition, the Leinster man is much more
proficient at these longer attempts. In short, O'Gara, at this
stage of his career is just an average long range kicker, while
Sexton is very good. However, the reverse is true at distances
shorter than 40 metres, although the gap in performance is narrower
than at longer distances. Both are above the group average, but
this time it is the Munster man who comes out on top.
Sexton lines one up
Moving down to those who underperformed in the limited dataset,
we find a mixture of seasoned kickers and young players.
Priestland's presence possibly shows how Halfpenny became Wales'
fulltime kicker, rather than simply their long range specialist.
The Scarlets player failed to match the average group expectation
at all distances, although the figures are likely to be less
extreme in a larger sample.
The presence of younger players in this under achieving
selection should be expected. Age appears to be a significant
factor in a kicker's development. From the data presented, a
typical under 20 player would be expected to hit a 54 metre
conversion 27% of the time from in front of the posts, compared to
38% for a typical Aviva Premiership kicker. The size of the talent
gap begins to narrow for central kicks as we move closer to the
posts and from 20 metres out the gap is down 95% for seniors
compared to 91% for younger players. Tentatively we may conclude
that the difference is at least partly down to less leg strength,
rather than lack of talent for the younger group.
This analysis illustrates how simple numbers can be used to
enhance visual and anecdotal evidence. Kicker development can be
evaluated more easily, along with strengths and weaknesses which
can then be used to target improved performance.
Perceived wisdom can also be tested. It is commonly supposed
that right footed kickers are better able to convert touchline
kicks from the left than from the right because the natural
trajectory of the strike is towards the posts in the former
case. Using this data there is a small, but statistically
significant difference between conversion rates from different
sides of the pitch amounting to about a 2% improvement when a
kicker kicks from his more "natural side".
We can also begin to investigate whether Southern Hemisphere
kickers have a better record than a similar group of northern
hemisphere counterparts, either through better skills or the
advantages of occasionally kicking at altitude. Super 15 kickers
did record slightly better records than their Aviva counterparts,
but not by a significant amount.
The ultimate aim of such studies is to provide more informed
decision making during matches. Players and teams are obviously
making such decisions already, such as declining to kick for points
if the kicker feels the distance is beyond his boot strength, but
Opta are making quantify such decisions achievable.
If a coach had accurate information on his kicker's likely
success from a certain point on the field, it is a simple process
to convert this to a point expectation for that kick. For example a
penalty with a 50% chance of success has a point expectation of 1.5
points. If instead the decision was made to kick to touch for a
lineout near to the opponent's try line, this new phase of play
would have to yield a try around one time in ten attempts to make
the new decision equivalent in terms of the average expected points
of the kick attempt. Such decision making processes, where the risk
and reward of different decisions are evaluated and balanced are
fast becoming an accepted way of coaching in similar sports such as
Most importantly, from a spectator viewpoint, these numbers can
settle arguments and by more accurately rating kickers by kick
difficulty we can confirm that Jonny Wilkinson remains a kicker of
the highest quality.
To learn more about OptaPro's Rugby SuperScout product,
please click here.