Last week, this column introduced a simple model that predicts how likely a shot is to result in a goal. Based upon descriptors such as distance from goal and if the shot resulted from a header, and trained with all of last year's MLS shooting data collected by OPTA, we were able to compare each player's goal total to the amount of goals that the player was expected to score based upon the quality of their opportunities.
From this comparison, conclusions may be drawn about which players were the most efficient goal-scorers and which players are on the receiving end of the most high-quality scoring chances.
However, not all the credit for goal scoring opportunities can be placed solely on the shoulders of the attacking team. More often then not, the defensive team deserve a little bit of blame for allowing the attempt at goal. So instead of looking at which players tend to encounter the most high-quality scoring opportunities, we are going to look at which teams tend to concede the most dangerous situations.
One of the benefits of this approach is that it partially controls for the strength of the shooter. As demonstrated last week, Thierry Henry is one of the most efficient strikers in the league. The three shots that he scored against Montreal had 13 percent, 9 percent and 31 percent chances of being scored by the average MLS shooter. Without the clinical Henry finishing, Montreal's expected goals against for these three shots is less than a single goal (0.53 goals, to be exact).
In this model, Montreal is punished for the quality of the chance that they conceded – not the quality of the opponent converting the opportunity.
|Games Played||Goals Against||Expected Goals Against||Expected Goals Against Minus Actual||xGA / Games Played|
|New York Red Bulls||7||14||8.57||-5.43||1.22|
|Real Salt Lake||8||8||11.10||3.10||1.39|
Even after suffering their first loss of the season, Sporting Kansas City top our defensive chart, conceding the least amount of expected goals per game at 0.86. Perhaps what is even more impressive is that alongside having the lowest expected goals against per game in the league, they have conceded 3.91 less goals than they would have otherwise been expected to concede. Sporting Kansas City is not just conceding the least amount of quality chances in the league – they are also incredibly adept at avoiding goals from the rare high-quality situations that they do concede.
But, looking further down the chart, we have some less intuitive results. Toronto FC and New York Red Bulls find themselves conceding 5 more goals than they were expected to concede. This suggests, for reasons not identifiable by this model, that the opponents of Toronto and New York have been considerably more clinical in their finishing than they would have regularly been expected to. What would cause this discrepancy?
Despite some of the anomalies, expected in any imperfect analysis, finding the current Eastern and Western Conference leaders at the top does lend this analysis some degree of merit. To conclude on a clichéd old adage: Offense wins games, defense wins championships.
Devin Pleuler is a computer science graduate from Wentworth Institute of Technology in Boston, where he played on the men's varsity team as a goalkeeper. He's certified as a coach through both the USSF and NSCAA, and writes the Central Winger analytics column for MLSsoccer.com.