What is expected goals (xG)?
Expected goals are a hot topic in the soccer community. Basically, every goal scoring chance has a statistical percentage (derived from thousands of historical shots and filtering them based on factors such as distance, type of shot, type of pass, etc. ) that it actual turns into a goal. For example, from all penalties taken in the Premier League, it turns out that 78 percent is converted into a goal. Therefore, the xG for a penalty will be 0.78.
All chances added to another will give the total xG for a team in a match.
Take Everton against Bournemouth in the picture below. The game ended in a draw 2-2, however the expected goals stated 2.5-0.5, meaning that a draw is not really deserved.
In conclusion, expected goals is a metric which assesses the chance of a shot becoming a goal.