Would you like to know the biggest joke in baseball? It’s a knee-slapper.

In a game where the likes of Jaret Wright and Eric Milton are signed to $20 million deals, how much would someone be worth if he could, all by himself, lower an entire staff’s ERA by three-quarters of a run? Keep in mind that 0.75 points of ERA is, over the course of a season, worth 120 runs, which is roughly equivalent to swapping Johan Santana’s 2004, in which he went 20-6 with a 2.61 ERA, for Casey Fossum’s, in which he went 4-15 with a 6.65 ERA.

The baseball market has provided the answer: Somewhere close to the major-league minimum player’s salary of $316,000.That is what Atlanta pitching coach Leo Mazzone is reportedly earning.

In the still-lingering aftermath of Michael Lewis’s “Moneyball,” there is much talk of market inefficiencies in baseball. The Oakland Athletics think that defense is undervalued in the market, and they stock up on it at what they feel to be bargain-basement prices. The Arizona Diamondbacks think that solid veterans are undervalued, so they acquire reliable players like Shawn Green and Russ Ortiz. The St. Louis Cardinals and Boston Red Sox employ analysts who fix a precise dollar values to every professional player, then attempt to acquire players who are, according to these formulas, worth more than they have to be paid.

Such efforts are certainly worthwhile, but seem a bit beside the point in light of Mazzone’s work. Rigorous studies have found that Braves pitchers consistently improve when they come under Mazzone’s tutelage and decline when they go elsewhere, to the tune of about 0.75 runs worth of ERA, even after you account for age, park and league effects, defense, and other outside influences.

The record speaks for itself. Washedup pitchers like John Burkett and Mike Hampton became strong no. 2 starters on Mazzone’s watch, as did the previously mediocre likes of John Thomson and Jaret Wright. Relievers like Chris Hammond and Kerry Ligtenberg, marginal at best with other teams, have been key cogs in a consistently solid bullpen.

Certainly there is a selection effect – the Braves’ front office has a keen eye for which pitchers to acquire and a keen sense of when to let them go. Still, arbitrarily halve the Mazzone effect and it remains comparable to the difference between Santana’s 2004 and Javier Vazquez’s.

To put it another way, I think coaches represent the single biggest market inefficiency in the game and the greatest opportunity for a team to improve itself at minimal cost. It’s hard to dig up information on how much exactly pitching coaches earn, but Mazzone was last reported by the Atlanta Journal-Constitution to have earned $200,000 during the 2002 season, after which he received a significant raise. If it was doubled at that time, Mazzone would be earning about $87,000 more than the league’s minimum salary – the biggest bargain in the game, and one that leads to some questions.

If the Royals can afford to pay Jose Lima $2.5 million to run up an ERA of 8.13, why not try to lure Mazzone westward by offering to increase his salary five-fold, or even more? Going by the general rules of thumb that 10 runs are worth a win, and a win is worth about $2 million on the baseball market, then Mazzone’s skills could be said to be worth somewhere between $10 and $20 million a year. At the very least, he should be paid more than Jose Lima.

While Mazzone is probably the most extreme example of what a coach can do for a club, he’s not alone. Look around the game at surprise teams, and you’ll quite often find a coach with a simple and coherent philosophy that allows him to get the most out of marginal talent.

In Milwaukee, for instance, Mike Maddux – who has for years been credited by his little brother Greg as having the real mind for pitching in the family – has done astonishing things. The Brewers’ ERA of 3.51 is fourth-best in the majors this year, and that with ace Ben Sheets missing more than half his starts with an inner-ear infection. No-names like Chris Capuano (3.01 ERA) and Victor Santos (2.73), who don’t have particularly impressive stuff and were never regarded as promising prospects, are pitching like aces. Of the Brewers’ eight relievers, one has an ERA over 3.20.

Maddux’s pitchers have been quite explicit in crediting him and his staff with their success. Doug Davis, who was released twice in 2003, arrived in Milwaukee sporting a career ERA of 5.06.A soft tossing lefty who throws two pitches, neither of them much better than average, Davis proceeded to pitch 207 1/3 innings with a 3.39 ERA last year, and sports a 3.89 ERA this year. The catalyst for Davis’s improvement? An adjustment consisting of raising his glove hand a few inches. He told the Milwaukee Journal-Sentinel last year that “[Maddux] simplified my mechanics and made it seem a lot easier.”

Such talk can sometimes make one’s eyes glaze over, but Davis’s strikeout rate has increased by nearly half under Maddux; that doesn’t just happen without coaching. The Brewers have had many such success stories, which come back to Maddux’s simple philosophy of “pitching to contact,” which means, as Mazzone preaches, locating the ball where the hitter can’t hit it hard.

As Maddux explained to the Journal-Sentinel, “If you can command the baseball and change speeds, you can win in the big leagues and that’s the biggest thing. If you command the baseball, you command the at-bat and if you command the at-bat, you command the inning. You command the inning then you command the game.”

Combine a common-sense approach like that with an ability to get players to buy into it, and you have a coach who can make marginal talents into solid regulars and a huge talent like Sheets into an elite pitcher. That’s worth a lot of money, and Maddux, who joined the Brewers in 2003, is a major reason why the Brewers are among the game’s fastest-rising teams.

An even more surprising team is the Rangers, who for a second straight year find themselves in hot pursuit of the AL West title. Considering the team is 17th in the majors in ERA, it might come as a surprise to hear about their pitching success. But the Texas rotation has a 3.97 ERA, and – more importantly – the staff as a whole has a 3.95 home ERA. That’s shocking because their home park, Ameriquest Field, has been one of the most hitter friendly parks in the game for years, annually inflating scoring by 10% or more.

The secret for the likes of Chan Ho Park and Chris Young has been the sinkerball preached by coach Orel Hershiser, who had a career of near-Cooperstown caliber simply by throwing the ball over the plate and letting hitters beat it into the ground. Take Park, who in his salad days with the Dodgers was a groundball pitcher, then lost his velocity and became a flyball pitcher with the Rangers. In 2003, Park actually allowed more flyballs than grounders, a recipe for disaster in that park. This year his GB:F ratio is back up to 1.36, and not coincidentally he’s having his first decent year with the Rangers.

Since joining the Rangers in 2002, Hershiser has been impressing on his charges the necessity of preventing the home run by throwing pitches hitters can’t drive. It’s not a foolproof plan, and not every Rangers pitcher has seen dramatic improvement under Hershiser, but the team has been winning in large part because their pitchers are finally able to keep them in games.

What Hershiser has in common with Maddux, Mazzone, and other notable coaches like Baltimore’s Ray Miller is an ability to make even marginal pitchers trust their stuff enough to throw it over the plate. As simple as it sounds, that’s worth an incredible amount; more, maybe, than Johan Santana.