Expected Runs in Finnish Baseball
This work proposes a discrete-time Markov chain model for the game of Finnish baseball (pesäpallo). In the model, the state of the game at the start of a hitter’s plate appearance is defined by the locations of the base runners and the number of outs. The game dynamics are described using discrete state transitions, with transition probabilities estimated from play-by-play data. Runs are tracked using special pass-through states that are entered whenever runs are scored. The model can be used to estimate, for example, the expected number of runs for the remainder of the inning, the added value generated by a player’s plate appearances, or a team’s win probability given the score and game state.
There are two perspectives for modeling expected runs in Finnish baseball: the team level and the player level.
At the team level, expected runs serve a role similar to expected goals (xG) in soccer or ice hockey. Each plate appearance is treated as a scoring opportunity, and its quality is measured by the expected runs directly resulting from that at-bat. This yields a metric that can be aggregated over multiple at-bats to assess the team's overall offensive performance. However, this metric should not be used to evaluate individual batters, since they have no control over the initial conditions of their appearance—such as the number of runners on base or the number of outs.
At the player level, performance is evaluated based on the expected runs (xR) the team is projected to score during the remainder of the inning after the player’s plate appearance. This means a player’s value includes not only the runs scored during their at-bat but also their contribution to setting up future scoring opportunities. For instance, a batter who comes to the plate with the bases empty is expected to reach first base rather than score directly. On the other hand, the player-level expected runs need to take into account the situation where the at-bat takes place. It is easier to score runs when the runner is already at third base.
In the following, these two perspectives are discussed further in Finnish.
Team-level Expected Runs (in Finnish)
Example analysis of team-level expected runs presented in Finnish.
Example analysis of player-level expected runs presented in Finnish.
Co-authored with Aku Kettunen.
