Conversion Rates

In baseball, basketball, football and other team sports there are established success / failure rates that define the game and those who play it.  In baseball a Batting Average of .300 or 3 hits in 10 at bats establishes one as a great hitter or an Earned Run Average of 3.00 per nine innings establishes one as a great pitcher.  In basketball converting on 50% of field goal attempts or 33% of 3 pt field goal attempts are standard measures of success / failure.  In football averaging 5 yards per carry is an accepted measure of success for a running back.

What about success / fail rates in soccer?

I had once been told that converting 1 of every 10 shots on goal was an acceptable rate of conversion in soccer. A shot on goal being defined by the NCAA Soccer Statisticians Manual as being a shot on net (see Section 3, Article 3). An article at Soccer Analysts  makes a case for a rate of 10.8% or one goal in every 9.25 shots on goal with a median of 1 goal in every 11 shots in the 4 professional European leagues they tracked. So, 1 goal from every 10 shots on goal wasn't a bad number.

Now, if we refer back to the definition of a shot on goal we discover that "results of a shot on goal must be either a save by the goalkeeper or defending team or a goal by the attacking team. This would indicate the save percentage for goalkeepers should be fairly high and if we check the MLS statistics we find typical save percentages for starting goalkeepers consistently in the low 70's percentile range. 

I have never quite bought into the 10% conversion rate for scoring goals. In the interests of consistency and fairness I took a look at MLS conversion rates and discovered the top goalscorers are actually converting at a far higher rate than 10%.  In 2012 leading goal scorer Chris Wondolowski converted on 27 of 55 SOG or an eye opening 49% conversion rate. The league conversion rate was 29.8% or nearly 3 of every 10 SOG resulting in a goal scored.

It would seem logical to look at what percentage of "shots" are actually "shots on goal".  This number is actually quite low at 25.6% for the 2012 MLS season or a little better than 1 of every 4 shots taken are actually shots on goal. If we look at the conversion rate of goals in the context of total shots taken the number drops all the way to 7.6% which is a little worse than the 1 in 10 number originally quoted to me.

What does it all mean?

I am reminded of hockey great Wayne Gretzky's quote, "You miss 100% of the shots you don't take."

Quite simply, one must shoot if one wishes to score, but accuracy of shooting (shots on goal) is extremely important as the conversion rates referenced above attest to. The more shots taken that a player or team can put on goal the better the chances are for scoring. Common sense stuff, correct? 

No comments:

Post a Comment