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As a Season Drags On, Batters Chase More Bad Pitches

Robinson Cano swung at a higher rate of pitches outside the strike zone in September 2012 than in May.Credit...Doug Kapustin/Reuters

Even the best hitters succumb. The season marches on, game after game, and they begin to flail. Picky in spring, they are ever more undiscerning come summer and fall.

According to a study by researchers at Vanderbilt University, the further the major league baseball season progresses, the more often batters swing at bad pitches. The reason is uncertain.

In May 2012, Robinson Cano swung at 27 percent of pitches outside the strike zone. In June, that rate was 37 percent, then up to 41 percent in July, 36 percent in August and 37 percent in September. The three-time most valuable player Albert Pujols’s rate of errant swings went up every month last season from May (32 percent) through September (40 percent), except for a dip in July.

Dr. Scott Kutscher, a neurologist, and his colleagues used data from Fangraphs’ database for 2006 to 2011 to calculate the so-called O-swing percentage — the percentage of swings at balls outside the strike zone. The rate, they determined, rises steadily over the season. An increase of about half a percentage point a month was typical.

Based on the 2006-11 data, Kutscher also predicted results for 2012 and found that 24 of 30 teams had poorer plate discipline at the end of the season than at the start. Over all, batters swung at 29.2 percent of bad pitches in April and 31.4 percent of them in September, with monthly increases that varied slightly from the predicted curve on Kutscher’s graph.

With some teams, the difference was drastic. The Houston Astros, for example, had an O-swing rate of less than 26 percent in April and of 34 percent in September. At the other end of the scale, the 2012 San Francisco Giants actually improved their O-swing rate to 33 percent in September from 34 percent in April.

“It would be interesting to see if a team’s won-lost record goes down as they’re swinging out of the strike zone more,” Mets catcher John Buck said.

Kutscher’s numbers say nothing about how O-swing rates might correlate with won-lost records. As the Chicago Cubs limped to a 61-101 finish in 2012, their O-swing rate actually dropped to 30 percent in September from 35 percent in May. Vladimir Guerrero hit 429 career home runs and batted .318 while swinging at more than 40 percent of pitches that never entered the strike zone. On the other hand, the wild-swinging Astros wound up with the worst record in baseball last season, while the Giants improved their plate discipline and won the World Series.

Kutscher, a sleep specialist, says he believes the trend is related to fatigue, even if he cannot prove it. “A lot of factors go into the numbers, but that they’ve been so consistent year to year is striking,” he said. “There’s no instance averaged over a few years where teams vary much from this. This strongly suggests that fatigue is playing a role.”

Whether an overall O-swing percentage is high or low in a given year makes no difference, Kutscher said.

“Worsening O-swing percentages through the year have held up independently of the mean O-swing percentage,” he said. “Whatever the average over the year, it’s going to be better at the beginning and worse at the end.”

In 2012, the Mets’ O-swing rate increased to 30 percent in September from 26 percent in April, peaking at 31 percent in July.

Some players admitted to tiring, and to having it affect their play. “When you’re tired, yes, you’re probably more susceptible to swinging at pitches out of the strike zone,” Mets infielder Justin Turner said. But he couldn’t explain the steady deterioration over the course of a season. “I have good months and bad,” he said. “It goes up and down.”

Buck said he had not noticed a pattern. Still, he said, fatigue was an issue. “I’m wired to stay up until 2 a.m.,” Buck said. “If I do that and then wake up at 8 for a day game, that’s not where a ballplayer wants to be.”

Matt Adams, a first baseman for the St. Louis Cardinals, said he did not need any academic proof. “I swing at a lot of bad pitches,” he said, “so I don’t have to look at the numbers.” He could not say whether his judgment would deteriorate during the season. “This is my first full year in the big leagues, so I couldn’t attest to it,” Adams said. “But I think everybody feels tired at the end of the year..”

There are exceptions. Prince Fielder swung at 33 percent of the pitches he saw outside the strike zone in May 2012, compared with 26.7 percent in September, dropping in every month but August.

Could the increase in the major leagues’ average O-swing rate to 30.8 percent last year from 23.5 percent in 2006 have something to do with an increase in strikeouts over the same period? All that wild swinging suggests that poor strike zone judgment might be one factor, and that fatigue may play a role that players should consider.

“Athletes take great care in what they eat, how they train,” Kutscher said, “and to me, looking at the data, it also makes sense that they start thinking about how they sleep in the same way.”

Kevin Long, the Yankees’ hitting coach, who had not been aware of the trend, said he was not certain how to explain it.

“Why it happens, why they continue to do it, why it goes up like that, yeah, it’s a mystery,” Long said. “It’s not that we don’t see it, because we do. It’s not because we don’t harp on it, because we do. The fatigue thing is interesting, especially with a guy like Robinson who plays every day. But I’d have to research it, see what happens.”

A version of this article appears in print on  , Section D, Page 1 of the New York edition with the headline: As a Season Drags On, Batters Chase More Bad Pitches. Order Reprints | Today’s Paper | Subscribe

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