Dumbest GM in Baseball

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Originally Posted by boomboom

So if Pujols had a decent backup on his team, he wouldn't be as valuable as if Jones had no backup, or a Triple Type player.... just for example.

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Whoever the team has behind a player as a backup doesn't change the value of that player though. When comparing players, we need to compare them based on the value of what they themselves did, and comparing players to the same baseline (in WARP's case, replacement level), is one way to do that. Comparing players while taking into account who their actual replacement would be is unfair to those players.

Take two players of the same position on different teams - one who hits .300/.400/.500 and another who hits .280/.340/.450. The first player is obviously more valuable. His team, though, has a backup capable of hitting .280/.340/.450 himself, while the second player's team has a backup that hits .230/.300/.330. Does that change what those two original players actually provided to their team? No. The first player still gave his team more production than the second player.

I mean, take this to the extreme. A player hits .350/.450/.700 and his team is so outstanding that his back-up hits .330/.430/.600. Another player hits .270/.330/.430 and his team sucks so much that his backup hits .200/.230/.250. Is the .270/.330/.430 player more valuable than the .350/.450/.700 player? No way. The backups don't change the production of the starters.

yes but the backups change the value of that player.

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Originally Posted by boomboom

yes but the backups change the value of that player.

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No, they don't. If they did, in my example, the .280/.340/.450 hitter is more valuable than the .300/.400/.500, and the .270/.330/.430 hitter is more valuable than the 350/.450/.700 hitter.

They change the production that that specific team would get if the starting player went down with an injury - and that's the value of the backup player. They don't change the value that the starting player provides while he plays.

What happens if the productive hitter gets hurt, who replaces him?

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Originally Posted by boomboom

What happens if the productive hitter gets hurt, who replaces him?

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Whoever the backup is..

The drop of production, though is not reflective of the productive hitter's value, but the backup's value.

You can't use a replacement level in your argument if you are not willing to recoginize who the replacement is.

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Originally Posted by boomboom

You can't use a replacement level in your argument if you are not willing to recoginize who the replacement is.

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Replacement level is not the same as who a certain team's actual replacement player would be. Using a replacement level is a way to measure the value of two players that are on different teams using the same scale. A good way to think of it to get rid of the confusion of the term replacement" is to think of it as measuring how much a player is "above the average", except with the "average" a step below the actual average.

Using who the actual replacement player could lead to a situation where a clearly inferior player is considered more valuable than a clearly superior player, as my examples above illustrate.

Furthermore, we cannot actually compare a player to his would-be replacement because we don't know how that would-be replacement would actually perform given full-time play. We can estimate, but we cannot know.

But, for the heck of it, look at the case of Albert Pujols and Andruw Jones. If Pujols went down in 2005, he'd likely have been replaced by John Mabry, who hit .240/.295/.407 with an 81 OPS+ while giving poor defense. Jones would have likely been replaced by Ryan Langerhans, who hit .267/.348/.426 for a 101 OPS+ with good defense. This also leads to the conclusion that Pujols was more valuable. However, this is, of course, poor reasoning, because we don't know how Mabry and Langerhans would have performed if they played regularly, which is why it's better to compare players to the same baseline.