“Glue� guys, in baseball parlance, are the players whose oft-overlooked performance quietly holds winning teams together—and without which, presumably, the team would fall apart. Statisticians don’t buy that they exist, but psychologists do. And players and managers swear by them.

“He’s the scrapper,� says Charlie Manuel, manager of the defending World Series-champion Philadelphia Phillies. “The guy who plays every day. Who gets big hits. Hustles. He’s the guy who, in his own way, whether it’s quiet or spoken or whatever, he leads.�
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Ryan Howard of the Philadelphia Phillies

Jason Bartlett is a glue guy. Before he joined the Rays last season, Tampa Bay had baseball’s worst record in 2007, due greatly to having the majors’ worst defense. Then Mr. Bartlett came over from the Twins and took over the shortstop position. The Rays’ defense became the best in baseball last season and they reached the World Series.

Tim Wakefield, the Red Sox’s knuckleball pitcher, is a glue guy. As Boston’s pitching staff has evolved over the past 15 years—with youngsters coming, veterans going and pricey additions like Daisuke Matsuzaka not always delivering—the dependable constant has been Mr. Wakefield, a first-time All-Star this year at 42 who has made at least 15 starts each season.

As baseball enters the second half of the season Thursday, the top contenders all have a glue guy or two whom they attribute part of their success to. With the Tigers, it’s All-Star third baseman Brandon Inge, who not only has a surprising 21 home runs but is also hitting .348 in close, late-game situations. With the Yankees, as usual, it’s shortstop Derek Jeter, who owns the highest on-base percentage among the American League’s starting shortstops despite being its oldest (35). And the Phillies insist slugger Ryan Howard is a glue guy—despite not fitting the tag’s small, scrappy stereotype—because he quietly never takes a day off.

“They’re the reliable guys,� says Braves president John Schuerholz, “who, in the toughest of circumstances, in the biggest of moments, deliver the goods.�

The legend of the glue guy is an extension of the age-old question in sports over whether natural “winners� exist—players who are greater than their statistics indicate, who win in part because of their force of will or ability to perform under pressure. Whether it’s with superstars who make clutch plays or unknowns who have a knack for being in the right place at the right time, fans and observers ascribe special talents to these players—often exaggerating their actual contributions.

Michael Jordan famously said in a 1997 Nike commercial that he’d missed 26 potential game-winning shots. “He’s probably been successful about 50 times,� then-Bulls coach Phil Jackson said at the time. But when Mr. Jordan retired from the Bulls in 1999—seven months after making his iconic shot to beat the Jazz for the championship—the total number of game-winning shots he’d hit was 25.

Skeptical about whether winners exist, statistician Scott Berry of Berry Consultants studied the matter in 2005. Taking the statistics of more than 14,000 players who had played in Major League Baseball, he created a formula to find the ultimate winner: the player whose teams exceeded their win-loss expectations the most when he happened to be on them.
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Tim Wakefield of the Boston Red Sox

The winners’ winner? Dennis Cook, a journeyman lefty reliever in the 1990s. Several players whom fans widely regard as winners and glue guys did fare well: Mr. Jeter, the Yankees shortstop, was in the 97th percentile, and David Wells, a noted big-game pitcher in the 1990s and 2000s, was in the 99th. But the presence of the relatively unknown Mr. Cook at the top, Mr. Berry says, proves his point. “Announcers refer to players who just have the will to win,� he says. “The fact that he comes out on top pokes fun at that notion.�

But Mr. Cook does believe in glue. Although he admits he was lucky to bounce from one winner to the next—including the 1996 division-winning Rangers, the 1997 world-champion Marlins and the 2000 National League-winning Mets—Mr. Cook says his teams won in part because they invested in overlooked roles like middle relievers.

“A long man who eats up 100 innings a year, he saves the rest of your pitching staff,� he says. “Those guys don’t get recognized, but they’re every bit as important. Baseball people see that, but number-crunchers don’t.�

Psychologists say there is indeed a spill-over effect with glue guys that helps their teams win, one which goes beyond quantifiable contributions. John F. Murray, a sports psychologist
in Palm Beach, Fla., says that teams are much like fraternities or high schools in that players spend a massive amount of time in close proximity to each other. Because of this, “they’re constantly influencing one another,� he says. “One of the keys to confidence is social support and modeling. If you have some outstanding role models who deal with pressure effectively, that glue is going to spill out of the bottle and help everyone.�

A huge hole in the reasoning of glue believers is that it’s impossible to know in retrospect how teams would have fared without their glue players. For example, the Rays won 58% of their games (11 of 19) earlier this season when Mr. Bartlett, their slick-fielding shortstop, was out with an injured ankle. They’ve won 54% overall. But the first-place Phillies’ abundance of glue, according to both them and their opponents, appears to be what’s put that franchise over the top—just a few years after it had a reputation for underachieving. “It’s not about just one guy,� says All-Star second baseman Chase Utley.

The Phillies’ most-talented players also happen to be their glue guys, including Mr. Utley, who has led the majors the past two years in times hit by pitch, and Mr. Howard, who has played in 362 of Philadelphia’s last 363 games. Unlike many left-handed hitters over the years, he even refused to take a day off against Randy Johnson once last season.

“He’s definitely a leader, just by keeping his mouth shut,� Mr. Manuel says. “I call him the Big Piece. As in the big piece of the puzzle.�

… just another example of the benefits of sports psychology.