How good (or how bad) is Chelsea goalkeeper Robert Sanchez?

Save percentage is just one metric that directly evaluates a keeper’s performances. Goals Prevented is another. Goals prevented, simply put, takes into consideration the quality of shots a goalkeeper has faced, i.e. the quality of shots on target of his opponents, and with that information, measures how reasonable it is to expect a goalkeeper to save it. Keepers aren’t judged harshly when they face shots that have a high expected goal (On Target) (xGOT) value. Goals Prevented takes the on target xG value of all the shots a goalkeeper has faced, along with the value of all the shots he has saved, and finds the difference.

The higher the value, the better the goalkeeper. This, along with save percentages, are a more reliable way of evaluating goalkeepers. Goals Prevented numbers can be positive, or negative. A number closer to zero – either side of the number line – suggests an average, OK, goalkeeper. Obviously a number farther along on the positive side suggests a very good goalkeeper, you get the idea.

The Goals Prevented metric also tells a story about how good (or bad) a keeper’s defense is, in this case: Chelsea’s defense. As you can tell which goalkeeper is conceding just how many he should, more than he should, or less than he should. The most noticeable thing about Sanchez’s Goals Prevented numbers, is that in all his three previous full seasons, he has never conceded less than he has been expected to. This suggests that he has never been a deciding factor for his team between the sticks, which should not be held against him too much, as it is difficult to do as a goalkeeper.

In his first Premier League season for BHAFC, FBRef suggests the club was expected to concede 23.3 goals in the 27 games he played for them. This is a good defensive record for Brighton, as they should have been good for less than one goal conceded per game (0.86), but they conceded one goal per game, and ended up conceding 2.7 goals more than they were expected to, in the stretch of games Sanchez played. That again, is not indicting, as one goal conceded per game is still relatively good for a newly-promoted Brighton side and goalkeeper. That same season CFC, who won the Champions League, had a defensive record that was good for 0.8 goals conceded per game, to put Brighton’s numbers into perspective.