Tuesday, 16 July 2013

Gerhard Tremmel, An Above Average Keeper.

As the calendar meanders from the end of one season to the pre-season of another, the lull in on-field action allows for the handing out of awards to the statistical leaders from 2012/13. The extension of the usual percentage based statistics to include additional x,y coordinated data has widen the scope of the discussion as well as hopefully improving our grasp of where the talent may lie, but  simple shot and save percentage can still be a powerful tool.

The leader in save % for Premiership goalkeepers during 2012/13 was Everton's Jan Mucha, with an impressive 92.3% save percentage and languishing in last spot was Norwich's Lee Camp, who saved just 20% of the on target shots that he faced.

Of course the missing ingredients from this short list of the supposed best and worst of Premiership stoppers is the number of shots the two polar opposites faced. Munca faced 13 shots and saved 12, while Camp, depending on the source faced just five shots and conceded four times in three games, two of which were from the bench.

So the best and worst keeper, from a save % perspective were also keepers who faced relatively few shots on target. The average number of on target shots faced by a Premiership keeper in 2012/13 was a shade over 80. The raw table of save % admirably demonstrates the ability of very small samples to possibly produce extremes of good or bad percentages that may not be fully representative of the likely skill levels of an individual player.

The feast or famine of the small sample size is further demonstrated by the save % for Swansea's Gerhard Tremmel. He chases home Mucha with a save % of 81% from a below average number of shots in 2012/13, but had a Lee Camp like disaster the previous year when in a single performance at the Britannia he faced two Stoke shots and failed to stop either. In the absence of a numerical context, Tremmel has gone from last place to nearly first in just a season.

Because of the small sample problem, it is usual to impose a qualifying threshold for trials and ignore evidence below a certain number. Conceding two from two, even against a traditionally lethal Stoke, shouldn't be sufficient to condemn a keeper as the league's worst, but it is nevertheless information and we should try to use it to make an informed judgement about Tremmel's likely talent level.

Prior to his Swansea debut at Stoke, Tremmel had played in the Bundesliga, most notably at Energie Cottbus and least notably for Hertha reserves. Over 200 matches in an unforgiving position, therefore demonstrates a degree of competence, even if a single match in February of the 2011/12 season hardly allowed him chance to demonstrate that ability in the Premiership.

If we were ignorant of his career in Germany and Austria, his mere presence in a single Premiership game is sufficient  to mark him as a talented keeper. If, prior to his Swansea debut, we grade him as an average Premiership keeper, we are more likely to get close to an unknown keeper's later potential. Conceding goals to Crouch and Upson should only result in a minor downgrade, rather than overreaction to two events and demotion to the foot of the goalkeeping table.

In 2012/13 we have thirty times the amount of information on Tremmel, who played in 14 Premiership games, but is this sufficient to propel a journeyman keeper to the near top of the Premiership keeper standings ?  As with his 0% save percentage from 2011/12, we need to look at his 81% figure in the context of all the available information.

He is still at Swansea, therefore his Stoke performance wasn't considered typical of the levels Swansea think him capable of. So our slightly below average for a Premiership keeper conclusion is probably still valid. He faced around 60 shots in 2012/13, below the league average and well below a career figure, so we should entertain the idea that 81%, while closer to his true, likely save % than his duck egg from 2011/12 is still a figure that requires confidence limits. Only then can we be reasonable sure that the spread of our estimate of his ability encompasses what we may expect if he enjoys a long term run in the side.

In the absent of use shot location data and without detailed knowledge of Swansea's commitment to defence, 2012/13 should probably result in an updated opinion of Tremmel's ability that now places him as an above average keeper, but we don't yet have enough evidence to declare him even the best EPL keeper during last season.

Single season data, especially if the player isn't a regular is merely a sample of that player's average ability and one particular sample may fall well above or well below his typical performance levels. The limited evidence of Tremmel's 15 game Premiership career projects that his long term save% will most likely lie somewhere between 82% (which would be exceptional and unlikely if we included his Austrian/Bundesliga stats) and 71% (which would be more in keeping with his slightly above average standing as Swansea's number two keeper). A career path and current age when even keepers begin to decline, suggest he is a good, but not great keeper who is unlikely to be an upgrade on Michel Vorm, Swansea's current first choice.

Just as one bad day at Stoke doesn't make you a poor keeper, one good, possibly luck or shot location driven run in mid season doesn't make you the league's best.

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