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What is OPS? January 12, 2015

Posted by tomflesher in Baseball.
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Sabermetricians (which is what baseball stat-heads call ourselves to feel important) disregard batting average in favor of on-base percentage for a few reasons. The main one is that it really doesn’t matter to us whether a batter gets to first base through a gutsy drag bunt, an excuse-me grounder, a bloop single, a liner into the outfield, or a walk. In fact, we don’t even care if the batter got there through a judicious lean-in to take one for the team by accepting a hit-by-pitch. Batting average counts some of these trips to first, but not a base on balls or a hit batsman. It’s evident that plate discipline is a skill that results in higher returns for the team, and there’s a colorable argument that ability to be hit by a pitch is a skill. OBP is \frac{H+BB+HBP}{AB+BB+HBP+SF}.

We also care a lot about how productive a batter is, and a productive batter is one who can clear the bases or advance without trouble. Sure, a plucky baserunner will swipe second base and score from second, or go first to third on a deep single. In an emergency, a light-hitting pitcher will just bunt him over. However, all of these involve an increased probability of an out, while a guy who can just hit a double, or a speedster who takes that double and turns it into a triple, will save his team a lot of trouble. Obviously, a guy who snags four bases by hitting a home run makes life a lot easier for his teammates. Slugging percentage measures how many bases, on average a player is worth every time he steps up to the plate and doesn’t walk or get hit by a pitch. Slugging percentage is \frac{(\mathit{1B}) + (2 \times \mathit{2B}) + (3 \times \mathit{3B}) + (4 \times \mathit{HR})}{AB} = \frac{\text{Total Bases}}{AB}. If a player hits a home run in every at-bat, he’ll have an OBP of 1.000 and a SLG of 4.000.

OPS is just On-Base Percentage plus Slugging Percentage. It doesn’t lend itself to a useful interpretation – OPS isn’t, for example, the average number of bases per hit, or anything useful like that. It does, however, provide a quick and dirty way to compare different sorts of hitters. A runner who moves quickly may have a low OBP but a high SLG due to his ability to leg out an extra base and turn a single into a double or a double into a triple. A slow-moving runner who can only move station to station but who walks reliably will have a low SLG (unless he’s a home-run hitter) but a high OBP. An OPS of 1.000 or more is a difficult measure to meet, but it’s a reliable indicator of quality.


Holy Cow, More On Ruben Tejada’s OBP July 29, 2014

Posted by tomflesher in Baseball.
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Last night, Ruben Tejada once again hit in the 8th batting order position. In four plate appearances, he walked once, in the bottom 8th; there’s been some discussion that Tejada’s OBP is inflated by intentional walks being thrown to get to the pitcher’s spot, though that definitely wasn’t the case here because the next player was lefty specialist Josh Edgin. As expected, Edgin was lifted for pinch hitter Bobby Abreu, who grounded into a double play. (Hmm. Maybe that was the intent. But Abreu only has 3 GIDPs on 140 plate appearances this year.)

Tejada’s stats by batting order position show some patterns. As an eighth-position hitter, Tejada has 198 plate appearances, 34 hits, 2 home runs, 32 walks, and 31 strikeouts, for a .213/.354/.288 line. In other order positions, he has 128 plate appearances, 27 hits, 0 homers, 14 walks, and 30 strikeouts, giving him a .245/.320/.275 line. Let’s assume, for the moment, that that .320 OBP line is Ruben’s true mark. That means his mark at the 8th inning should be, with 95% probability, somwhere in the range of .320 +/- .066, or somewhere between .254 and .388. Obviously, .354 is in that range. In fact, the .034 difference is about 1 standard error out, meaning there’s about a 70% chance of achieving that mark by chance alone.

In other words, it looks like there’s a statistically significant effect for Ruben batting in the 8th position. If we remove Ruben’s 9 intentional walks received in the 8th position and replace them with 2 hits and 7 outs, we’re left with a truly terrible .297 OBP, which is surprisingly even worse than his OBP while batting elsewhere, and one within one standard deviation of his .320 mark. That is, of course, a worst case scenario, assuming he wouldn’t walk at all in those 9 appearances. If he walked 3 out of 9 times, as his other stats would indicate, that would put him at a still not great .313 OBP.

Tejada leads the team in OBP April 9, 2014

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Moneyball was an influential book for two reasons. First, it described the process by which a GM can attempt to min-max a winning team every year. That’s interesting. Second, it showed a lot of the fans – not the front offices, who had already corrected the inefficiency by the time the book was published, but the fans – about the importance of walking and generally getting on base.

I never thought last year that I’d be typing this sentence, but Ruben Tejada is leading the Mets in OBP for qualified players (3.1 plate appearances per team game). Two players outstrip Tejada’s .400 mark – professional pinch hitter Ike Davis and starter Jonathan Niese, each at .500 – but neither has enough plate appearances to be on pace to qualify for rate stats. In retrospect, it shouldn’t be surprising that Tejada’s eye is developing. As a 21-year-old in 2011, Tejada had an OBP of .360 in 376 plate appearances over 96 games, walking 35 times – that’s one walk every 10 3/4 plate appearances – and striking out 50, for a K/BB ratio of 1.42. Last year, Tejada went pear-shaped, walking only one out of every 15 plate appearances, but he still only struck out 1.6 times for every walk he took – which is hardly the mark of an inconsistent hitter. Last year, it looks like Tejada just got really unlucky, batting .228 on balls in play versus a team average of .291. This year, he’s swung all the way to the other side of the pendulum – so far, his BAbip is .400 versus a team average of .241.

Tejada may never be a brilliant shortstop like Jose Reyes was, but his batting is gaining in consistency.

Is A-Rod’s Performance Different? August 3, 2010

Posted by tomflesher in Baseball, Economics.
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In games between milestone home runs, is Alex Rodriguez’ hitting similar to other times? (This is all a very polite way of asking, “Does A-Rod choke?”) It’s difficult to answer, because there’s so little data about those milestone home runs. A-Rod, though, has some statistically improbable results and it would be interesting to look at it a bit more closely.

Over 2008-2009, Alex played in 262 games and had 1129 plate appearances with 281 hits, 65 home runs, a triple:double ratio of 1:50, an OBP of .397, and a SLG of .553. His OBP has a margin of error of .0146, so we can be 95% confident that over those years his baseline production would be somewhere between .368 and .426 and absent any time or age effect that is the range in which A-Rod should produce for any given period.

Two recent milestone home runs come to mind as examples of Rodriguez’s reputed choking. First, the stretch between home run #499 and #500 was 8 games and 36 plate appearances. (I’m intentionally ignoring extra plate appearances on the days he hit #499 and #500.) During that time, Alex had an OBP of only .306. That’s a difference of .091 over 36 plate appearances and that performance has a standard error of about .078 when compared with his regular performance, implying a t-value of about 1.16. With 35 degrees of freedom, Texas A&M’s t Calculator gives a p-value of about .127, so this difference is marginally within the realm of chance. (The usual cutoff for significance would be .05.)

A-Rod hit his last home run on July 22. Discounting the plate appearances after his last home run, he’s played in 11 games with a paltry .255 OBP and .238 SLG over 47 plate appearances. His .255 OBP has a difference of about .142 and a standard error of about .064. That implies a t-value of about 2.21, with a p-value of about .016. That is, the probability of this difference occurring by chance is less than 2%. That gives us one result as close to significant and one as probably significant.

As a side note, A-Rod’s Choke Index continues to rise. He’s gone 48 plate appearances without a home run, and at a rate of .055 home runs per plate appearance the probability of that occurring by chance is about .066. That leaves his Choke Index at .934.

The DH Redux: Japan June 7, 2010

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In an earlier post, I analyzed team-level data from Major League Baseball to determine the size of the effect that the Designated Hitter rule has on on-base percentage. The conclusion I came to was that, if the model is properly specified, the effect of the designated hitter rule is about .008 in on-base percentage. If the reasoning was correct, then when there are no other confounding variables, the effect should be similar in size for any other professional league.

Of course, the other major professional league is Nippon Professional Baseball, the major leagues of Japan. Since it produces players at a level similar to MLB, and the other factors are similar – the DH rule was adopted in 1975 by one, but not both, of the two major leagues – NPB is an ideal place to try to test the model I specified in this post.