Stats, where I get them, and a glossary
This is a blog dedicated to looking at the team through the lens of statistics. I personally love advanced metrics in baseball and I have seen some good ones being developed for (American) football. I don’t claim to always understand the math behind them, but I do think that stats can give great insight into how well or poorly teams and individuals are playing.
With that said, stats always need context and eye test should not be dismissed. My general goal is to always back up what my eyes tell me about a player or team with stats and if there is a discrepancy, I try to figure out why that is. As I am not a professional journalist and don’t have time to watch every single MLS game, I will definitely lean on stats where I don’t have “eye test data” (if you will accept the phrasing).
As a rule, rating systems are some of my least favorite data points (think PFF in American football or WhoScored in the case of soccer). With that said, I do think more data points are always better and I will make use of them at times. I make no sweeping judgements about any system or their validity, nor do I assert they are the end all be all. As with any other stat, I try to use them in context and as one point of reference for coming to conclusions.
Some common stats that will be used:
xG = expected goals. xG is the probability that a shot will score. Location of the shooter, body part, type of pass, type of attack will all factor in.
npxG = non-penalty expected goal. nxpG excludes penalty kicks, since they have a high standard xG (always 0.76).
xGA = expected goals against. Basically, how many goals a team would be expected to give up based on the xG they face.
xA = expected assists. xA is the xG which follows a pass that leads to an assist.
PSxG = post-shot expected goals. PSxG is how likely a goalkeeper is to save a shot. It is only calculated for shots on target.
PSxG/SoT = post-shot expected goals per shot on target. A higher number means that shots are more difficult to stop.
PSxG+/- = post-shot expected goals minus goals allowed. Positive number indicate that a goalkeeper has an above average ability to stop shots or it can indicate luck.
Launch% = launch percentage. Percentage of passes that were "launched," meaning, kicked longer than 40 yards. Does not necessarily include goal kicks. There is a Launch% for goal kicks and non-goal kicks.
A good explanation for many of these stats can be found on FBref, here.
Different websites also get their data from different sources. For example, FBref gets their information from StatsBomb, while Squawka gets theirs from Opta. For the most part, I find the information to be pretty similar. There are times when there are discrepancies and I will note that. I also try to get all stats from the same place when comparing players (e.g., if I'm look at pass percentages of players, I try to get all of it from FBref, rather than one player from Squawka, one from FBref, and one from MLS stats). My preference for hard data is FBref for no other reason than I find the site easily navigable.
At the end of the day, I am an amateur. I will probably get things wrong from time to time (e.g., misunderstanding a stat, misusing a stat). If I do, let me know!