Friday, May 29, 2009
Question of the Day, 05/29
(Note: I’m going to be moving all the posts from the other thread to this one, as it’ll be a jumble otherwise. If I missed one, let me know.)
FROM MGL:
Runners on first and second and 1 out and you are the batter. The count is 3-2. The pitch is on the way and it is marginal. You estimate 50% ball and 50% strike. Swing or no swing? It might depend on the inning and score (and other variables), but we’ll assume that we don’t know anything else.


Which leads to the next question:
No swing: 50% chance of bases loaded, 1 out; 50% chance of 1st and 2nd, 2 out.
Original run expectancy: 0.97
RE of bases loaded, 1 out: 1.65
RE of 1st and 2nd, 2 out: 0.47
Average: 1.06
source
All right, now what if you swing. Obviously if you are a very bad hitter you should not swing. What if you are Albert Pujols? When he swings at a pitch not in the zone, he makes contact 65% of the time. When he swings at a pitch in the zone, he makes contact 92% of the time. The average is 79%. (source) So if he swings at this pitch he will strike out 21% of the time. In that case the linear weight would be -0.53. (source; from the above we would expect -0.50, so -0.53 is close enough)
If he makes contact, it might be a foul ball, non-foul out, which puts us right back where we started. If it is a BIP, let’s be generous and give him his overall BIP numbers. (Generous because this pitch is worse than the average pitch he swings at.)
single: 21% ... linear weight = +0.88
double: 8% ... LW = +1.54
triple: 0% (rounded down) ... LW = +1.90
HR: 8% ... LW = +2.39
ROE: 1% ... LW = +0.99
BIP out: 62% ... LW = -0.60
source for percentages
source for LW values
The weighted average LW = +0.14. So we have
Strikeout: 21%, LW = -0.53
Foul: X%, LW = 0
BIP: (79-X)%, LW = +0.14
Even if X=0, the overall LW is right around zero. For realistic values of X, the overall LW is negative. Compare to +0.09 if he does not swing.
Therefore, even Pujols should not swing. Neither should anybody else. Once you throw in game theory, it may make sense for the hitter to swing some of the time, but in a single situation the answer is no.