Thursday 29 October 2015

The Penalty Shootout Kings are Stoke City.....and Chelsea.......and Kidderminster.

Stoke City moved imperiously into the quarter finals of the only major trophy they have lifted in their 152 year history.

The Capital One Cup is a butchered version of the prestigious trophy the Potters lifted back in 1972 and with the delayed entry of the more preoccupied Premiership heavyweights and a truncated format, Stoke have reached the last eight by winning just once in open play.

Their two successful penalty shootout victories have not only set up a home tie with Sheffield Wednesday, it has also projected them to a respectable 50% success rate in penalty kick tiebreakers.

Meanwhile defeated visitors, Chelsea now have breathing space to consolidate their position in mid table, while seeing their success in shootouts fall to 40%.

Of course percentages are largely meaningless, obscuring more instructive information, such as sample size. Chelsea has won one more shootout than Stoke, 7 compared to 8, but Stoke has had 6 fewer opportunities, 14 compared to 20 and has in raw terms been more efficient.

Therefore it is understandably that the Daily Mail was spoiled for potential headlines when they presented Opta's breakdown of historic penalty shootouts for England and Wales' club sides. Eventually plumping for Liverpool as the most efficient as well as the most numerically superior of the current Premiership sides. (Another imaginary feather in Klopp's cap).

The article does an admirable job of presenting fascinating trivia, especially following a week where so many matches were decided from 12 yards.

Records are presented as just that, with percentages invariable going hand in hand with sample size and only once does the article over stretch when attempting to equate success rate to raw ability. Kidderminster (0-3) are declared worse than Newcastle (1-9).

Jose decides who will spin the coin for him at Stoke. (I'd perhaps give Kenedy a miss, Jose)
Penalty shootouts are often declared a lottery, although with success rates for an individual kick at around 80% rather than 1 in 14 million, a coin toss would be a better analogy.

An individual penalty kick requires the application of the most basic of footballing talent. To propel the ball forward twelve or more yards with as much power or guile before the keeper (Begovic) can remember which is your favoured side.

Therefore, while open play demands a much more varied array of talents, as well as combined team inter play, penalties are more likely to see a similar level of ability from those taking or attempting to save each attempt.

With luck and talent being ever present contributors to a sporting outcome, when talent is likely to be of a very similar and high level, as it may be in a penalty shootout, then luck will become the major factor in success or failure.

The spread of successes in raw and percentage terms, will range from the bad/unlucky of Newcastle and Kidderminster to the good/lucky of Brentford and Liverpool. Kiddy's 0 from 3 has around a 13% chance of happening by (bad) luck to a side that has taken part in three 50/50 contests. Newcastle's 1 from 9 is around a 2% chance if they too had played out nine evenly matched contests.

However, Opta's penalty shootout roll call contains 133 different sides, which increases the chances of finding a side as "bad" as Newcastle appear just by chance.

If we look at the spread of outcomes for all 133 teams, taking into account number of shootouts and efficiency we can find how much we need to regress the actual record of each team towards the group average success rate of 50%.

And with the data available so far you should regress all the way to 50%. Newcastle's 11% success rate from 9 attempts likely hides an underlying talent level that is very close to 50%. The same as Brentford who has won 14 from 23 at 61% ........ and every other team who has ever taken a penalty shootout in anger.

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