Mains: What does a WARP less than zero mean?

From SABR member Rob Mains at Baseball Prospectus on March 5, 2020:

The part of WARP that is murky, or confusing, or infuriating, is the RP part. (Or, if you prefer, the R in WAR). The idea of a “replacement player” is understandable in abstract. It’s the average player you can pluck from AAA to fill a need. It’s harder to understand in practice. Who, exactly, is this replacement player? Last April 21, the Yankees put Aaron Judge on the 10-day injured list with an oblique strain. They called up Thairo Estrada from AAA. Does that make Estrada a replacement player? Well, no, he certainly wasn’t for Judge. He didn’t start a single game in right field.

But as it turns out, he was pretty replacement player-y during the 2019 season for the Yankees. He was called up and sent down three times. (He might’ve done a fourth round-trip from New York to Scranton/Wilkes-Barre but for a hamstring strain.) He got 69 plate appearances in 35 games, contributing 0.1 WARP—about zero. He fits the bill.

But that’s the exception, not the rule. The Orioles traded for Tom Eshelman in June and called him up on July 1 for a spot start, then for a month after July 14 when David Hess got sent down. He was a closer to a literal replacement player. But he didn’t match the theoretical ideal: He generated -1.2 WARP. He was worse than replacement. Sometimes a full-time player is below replacement. Albert Pujols had -0.1 WARP in 2017, when he had 636 plate appearances.

Read the full article here:

Originally published: March 5, 2020. Last Updated: March 5, 2020.