Thursday, January 28, 2010
Day-off risk vs. catastrophe risk
Posted by Jonathan Halket at 6:20amLots of high-skilled players get big discounts due to injury concerns. Ben Sheets, Rich Harden, and Mike Lowell are just a few of the candidates for the sale rack. The big question is: Just how much of a discount should you apply to these types of players?
Some projection systems, like CHONE and Marcel, forecast playing time (in games or plate appearances). Expected playing time figures heavily in these systems' forecasts for the players' counting stats. The more the system expects the player to play, the more runs it expects the player to score (everything else equal, of course).
It is well known that, for fantasy purposes, one should add in the contributions of a replacement-level player when computing a player's value. So, a player that is forecast to score 100 runs in 100 games is worth more than a player forecast to score 100 runs in 162 games. Why? Because you'll be able to play a replacement player for at least some of the games that the 100-game player is forecast to miss. That player's going to score some runs too.
This is one reason why "real-life" baseball valuation stats, like Wins Above Replacement, figure value relative to a replacement player. Of course, since replacement levels in fantasy are so dependent on how deep your league is (in number of teams, bench size and number of positions used), these kind of replacement-level calculations are usually left up to the user.
The temptation is to do something like the following: Let's say the generic replacement-level player in your league is projected to earn 0.3 RBIs per game. Next, you take, say, CHONE's forecast of 72 RBIs in 122 games for Mike Lowell. Then you compute the expected RBIs from drafting Lowell as 72 + .3 x (162-122) = 84.
Unless you're in a daily league (and probably even then), it is unrealistic to expect to be able to replace Lowell in your lineup the minute he gets injured. So you'd like to apply a discount—maybe instead of assuming the replacement player plays 40 games, you assume he plays only 30 games for you.
I'd argue that the discount that you should apply to injury-concern players should vary a great deal depending on the player (and the injury). John Smoltz may be projected to start 20 games while Sheets is projected to start only 19, but I think you should apply a bigger discount to Smoltz, particularly in weekly leagues. Why? Because Smoltz is far more likely to have a start unexpectedly skipped, giving you a big fat zero in his spot for that week. Whereas Sheets is likely to be already comfortably nestled in your DL spot for the bulk of the starts that he might miss. Same thing applies for Chipper Jones versus Alfonso Soriano.
Pure speculation: If you're looking for some hidden value, I think the players that are catastrophic injury concerns, like Sheets, may give you a little extra profit over players like Harden, who are more likely to have nagging injuries. I bet that lots of fantasy players discount too heavily players that are at risk for season-ending injuries versus players that are given lots of extra days off.
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I like this approach to conceptualizing injury risk.
The fact is, “catastrophes” can’t be predicted, so inferring 120 games for a “catastrophe prone” player either dramatically overvalues or undervalues that player - it certainly does not “get it right.”
But we have a bit more predictive power over chronic or nagging injuries, and can more accurately guess the value of a Chipper Jones or Milton Bradley type.
To me, that means taking a chance on Ben Sheets is much more likely to pay dividends than on Rich Harden, given that on draft day Harden’s contribution is more likely to be properly valued.