Before the season, I put up a three-part series (1, 2, and 3) that explained how linearly-weighted stats like wOBA, while useful for comparing players to each other, don’t necessarily reflect each player’s true contribution to their team’s run scoring. You see, the weights used to calculate wOBA are based on league averages. So, for a team with league average breakdowns in walk rate, singles rate, home run rate, etc., wOBA (and its offspring, wRC+) ought to work very well in figuring out how valuable a player is (or would be) to an offense. However, when it comes to particularly bad or good offenses, or to those with unusual breakdowns, wOBA will lose some of its efficacy.
Why? There are synergistic effects in offenses to consider. First of all, if a team gets on base a lot, there will be more team plate appearances to go around, which of course gives its batters more chances to contribute. Second of all, if the team gets on base a lot, a batter’s hits are generally worth more, because they’ll tend to drive in more runs. And, of course, once the batter gets on base in such a team, it will be likelier that there will be a hit (or series of hits) to drive him in. The reverse of all three points is true in a team that rarely gets on base.
But it goes even beyond that. Let’s say Team A gets on base 40% of the time, and Team B gets on only 20%, but their balances of the ways they get on base are equal (e.g. each hits 7x as many singles as they do HRs) . A home run is going to be worth something like 14% more to Team A, due to more runners being on base. However, to Team B, a home run is worth over ten times as much as a walk, whereas to Team A, it’s worth only about 5 times as much. That’s because Team A has a much better chance of sustaining a rally that will eventually drive in that walked batter. Team B will be much more reliant on home runs for scoring runs.
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