Three months ago I wrote an article on the goalscoring characteristics of champion and relegated teams, and showed that champion clubs in general have very tight and consistent defenses. In particular, the goals allowed variance -- the spread of the individual numbers about the average goals allowed -- tends to be less than 1.0 for the top teams, which means that the standard deviation is less than 1.0 goals/game. (Standard deviation is the square root of variance.)
Now that the 2011 MLS regular season is over, it might be useful to plot a similar chart of team goalscoring statistics.
Below are two plots -- the first shows a scatter plot of the mean and variance of goals scored by MLS teams, the second shows a similar plot for goals allowed. I've tagged each point with a three-letter code for a MLS team, and the key follows the figures.
(Key: CHI = Chicago Fire, CHV = Chivas USA, CLO = Colorado Rapids, CLM = Columbus Crew, DCU = DC United, FCD = FC Dallas, HOU = Houston Dynamo, LAG = LA Galaxy, NER = New England Revolution, NYR = New York Red Bulls, PHI = Philadelphia Union, PDX = Portland Timbers, RSL = Real Salt Lake, SJE = San José Earthquakes, SEA = Seattle Sounders FC, SKC = Sporting Kansas City, TFC = Toronto FC, VAN = Vancouver Whitecaps FC.)
There are several characteristics of the playoff teams that are borne out in the charts. The playoff sides generally score between 1.2-1.5 goals per game, but their offensive goal variances vary widely. Houston scored more than two goals in just four matches, while Chicago had a large number of matches in which they scored one goal and five in which they scored three (none in which they scored four or more). Seattle were the big outlier as they showed themselves equally capable of being free scoring and unable to find the back of the net. DC United were another outlier among non-playoff teams; their average goals scored is higher than LA's and exceeded by just three other teams (Sporting KC, NY Red Bulls, Seattle).
On defense, Los Angeles Galaxy were head of the class with 17 clean sheets, but their goals allowed variance crept above one thanks to two matches in which they allowed three goals and one in which they allowed four. Real Salt Lake's defense is just as good as LA's (14 clean sheets, 10 matches allowing one goal), but they allowed more than two goals in ten matches, equal with Philadelphia and Seattle. Houston had the lowest goals allowed variance in the league thanks to allowing one goal in 17 matches, but their inability to keep a clean sheet inflated their goals allowed average. DC United's defense proved to be a liability to the team's playoff hopes, and Toronto FC's defense was wildly inconsistent (they got on enough of a run to advance to the CONCACAF Champions League quarterfinals, though).
I know that the MLS Cup Playoffs -- and all postseason tournaments -- are randomizing events in a league season. But if goal defense characteristics are the same indicators of playoff success as they are of league success during the regular season, I'd expect a Galaxy-Union MLS Cup final. However, I am intrigued by the upcoming RSL-Seattle series and the impact of a Sporting Kansas City side that is much improved from the one that opened its new stadium in June.