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September 18, 2000

Tough Cops... and Other Ones

Stolen Base Rates by Umpire

by Michael Wolverton

Did you know that some umpires are more steal-friendly than others?

I have to admit, that possibility had never crossed my mind until a recent discussion on Usenet's rec.sport.baseball mentioned a couple of articles in previous years' STATS, Inc. books that addressed the relationship between umpires and stolen-base percentage. The earlier of those two articles showed a seemingly wide disparity between umpires on steals: some called out over 40% of would-be basestealers, while others called out fewer than 20%.

That got me wondering who the toughest and easiest umps to steal on are today. I looked at the combined numbers from 1999 and 2000 (through last Sunday's games) and considered only steal attempts of second base. Among umpires who worked more than 750 innings at second base, here are the five with the highest percentage of would-be basestealers called out:

Umpire            SB  CS    CS%
-------------------------------
Chuck Meriwether  55  41  42.7%
Paul Schrieber    47  35  42.7%
Mark Carlson      38  28  42.4%
Tim Welke         45  32  41.6%
Rick Reed         62  44  41.5%

And here are the ones with the highest percentage of safe calls:

Umpire            SB  CS    CS%
-------------------------------
Mike Everitt      59  11  15.7%
Ed Montague       72  18  20.0%
Jerry Crawford    55  14  20.3%
Angel Hernandez   87  25  22.3%
Wally Bell        59  17  22.4%

At first glance, it certainly appears that some umps are more prone to call a runner out on a steal attempt than others. Over a two-year period, Chuck Meriwether was about two-and-a-half times more likely than Mike Everitt to send a would-be basestealer back to the dugout. That CS% split is not all that different from the split between the most and least successful catchers over that same period--Ivan Rodriguez at 47.4% and Dave Nilsson at 14.0%, respectively (again, considering only steal attempts at second).

Is it possible that the differences are just due to chance, that there really is no "basestealing bias" among umpires? After all, both STATS, Inc. and I ran statistical significance tests on the data we used, and neither of those tests found a significant relationship between umpires and steal percentage. In this case, though, I think the significance tests got the results they did because the sample sizes weren't large enough, and other evidence points pretty strongly to the existence of the basestealing bias.

The first, and most compelling, piece of evidence: Doug Drinen, in the aforementioned newsgroup discussion, looked at a much larger collection of games in the 1980s, with the data courtesy of the wonderful folks at Retrosheet. He found that Terry Cooney called out 46% of basestealers, while Larry Goetz called out only 23%, each in over 550 steal attempts. That kind of disparity in that large a sample would be pretty much impossible if there were no relationship between umpires and steals.

Another piece of evidence pointing to a basestealing bias is that there is a positive correlation between the umpires' caught-stealing percentage between 1999 and 2000. The correlation is fairly weak (a coefficient of 0.26--not too surprising since we're talking about only around 50 attempts per umpire per year), but it's still strong enough to indicate there is a signal coming through the noise.

So, while there's plenty of work left to do to determine exactly how large and how prevalent the effect is, I feel safe stating that there is an umpire effect on CS%. And I feel safe concluding that the umpires in the first table above are, as a group, less friendly to stolen bases than the umps in the second table.

That brings me to the really interesting question: do major-league baserunners and managers do anything about it? Do they track the umpires' caught-stealing numbers, and then run sparingly on the tough umps and freely on the easy ones? Let's take a look at our two extreme groups again, measuring the frequency of steal attempts against them (expressed here as steal attempts per 18 half-innings worked at second base). First, the "Don't tread on me" crowd:

                     SB Attempts
2B umpire              per Game
----------------------------------
Chuck Meriwether         1.54
Paul Schrieber           1.35
Mark Carlson             1.58
Tim Welke                1.64
Rick Reed                1.78
----------------------------------
AVERAGE                  1.57

And now the "Buy first base, take second free" crowd:

                     SB Attempts
2B umpire              per Game
----------------------------------
Mike Everitt             1.56
Ed Montague              1.59
Jerry Crawford           1.41
Angel Hernandez          2.01
Wally Bell               1.37
----------------------------------
AVERAGE                  1.59

And there you have it: there's virtually no difference in the rate of steal attempts between the most steal-friendly and the most steal-hostile umps. Even though teams do pay close attention to catchers in their steal decisions (teams run against weak-armed Mike Piazza more than twice as frequently as they run against strong-armed Ivan Rodriguez), and even though umpires could have the same sort of effect on CS% as catchers, runners attempt steals against the toughest umps in the league just as often as they do against the easiest.

I don't want to make too big a deal of this. Even if runners and managers were to take umpires into account in their basestealing decisions, the benefit to most teams would be small, maybe a handful of extra runs per season. Still, given that teams have always tried to squeeze out every extra run they can through bookkeeping and strategy, it's a little surprising that this strategic opportunity has apparently escaped them.

Michael Wolverton can be reached at mjw@baseballprospectus.com.

Related Content:  Umpires,  Significance

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