What are expected goals (xG) in hockey?

We rate every unblocked shot by how often shots like it go in, looking at distance, angle, shot type, whether it came off a rebound or a rush, how many skaters each side had (3-on-3 overtime, a power play, a goalie pulled for an extra attacker, a penalty shot), and what happened just before it, such as a pass across the front of the net or a turnover. Add up a team’s or player’s shots and you get how many goals their chances were worth. A team that scores well below that ran into a hot goalie, didn’t finish or was unlucky. A game’s number is the model’s own; season tables scale each season’s shot values so the league’s add up to its actual goals.