The new Game Strategy Explorer tool on Baseball Savant allows you to find the win probability or run expectancy for any MLB game situation, based on data from the last 10 seasons.

This allows you to calculate how any play affects a team's win probability -- just take the difference from the "before" game state (the start of the play) to the "after" game state (the end of the play).

You can also explore how different player/manager decisions -- stolen base attempts, intentional walks, sac flies and sac bunts -- affect the win probability for a team.