When David Ortiz connected for his first home run of the season, in the middle of a six-run fifth inning that powered the Red Sox to Wednesday’s win over Toronto, he told reporters in Boston that for the time in nearly 40 games he looked “like a real hitter.” But if Big Papi is to keep poppin’ homers for the Sox, Ortiz may needs more than confidence: the solution could be to hit more ground balls.

Because batting average is an unstable statistic from year-to-year, the rate at which a player hits ground balls-to-fly balls (G/F) has become an important barometer for teams evaluating new prospects and current talent.
Earlier this season, Rays‘ manager Joe Maddon went public in his defense of having a separate fly ball batting average to keep specific tabs on each player’s frequency of airborne outs. Maddon used Jason Bartlett as an example, citing the shortstop’s lack of pure power as a primary reason to stress lower-trajectory balls.

But is there a specific G/F range that maximizes a player’s offensive potential? And how accurate is G/F in assessing home run hitters?
Let’s take a closer took, starting with Ortiz.

The slugger snapped his homerless drought at 149 at-bats, and looking at Ortiz’s G/F of 0.37, it’s little wonder why he has struggled mightily in the season’s first 40 games. Ortiz’s G/F was 0.58 last season and over the last four years he has averaged a 0.55, meaning the number of balls he’s putting in the air this season has skyrocketed.

So, why no homers? That’s easy. Most balls in the air that stay in the park are a product of swinging late or hitting the ball from underneath the zone. Naturally, Ortiz’s lower G/F should signify less line drives, and that number (down from 19 percent of balls batted in 2008 to 16 percent) supports the theory.

When Ortiz was averaging the most homers in 2006, one per every 10.3 at-bats, his G/F was 0.58 and his ground-out-to-fly-out ratio (GO/AO) was 0.90, which means he was splitting his outs fairly evenly. Not surprisingly, his GO/AO this year is a career-low 0.56.

Let’s look at what improved ground ball rates translate into in regards to Ortiz’s power.

              2006     2007     2008     2009
G/F           0.58     0.61     0.58     0.37
GO/AO          .90      .93      .84      .56
HR %          7.9      5.3      4.7      0.6
% FB/HR      20.9     13.6     12.6      1.5
RC/G          9.8     10.8      6.6      3.6

Using G/F and GO/AO rates from his last three seasons and comparing them to his start in 2009, you can see that Ortiz is a hitter that thrives when he is producing a relatively even amount of ground ball and fly ball outs. Although his fly ball to home run conversion rate drops from 2006 to 2007, where he had the highest G/F and most stable GO/AO, Ortiz’s run contribution increased, which could be a result of his higher batting average on balls in play (BAbip) up from .270 to .355. Using the Bill James formula which estimates runs created per approximately 27 outs, Ortiz’s contributions averaged 10.8 runs per game. That’s more than double his RC % so far this year.

Because Ortiz is 33 and has been struggling with wrist injuries and the usual decline that comes with old age, let’s now look at Yankees first baseman Mark Teixeira. The 28-year-old signed a $180 million dollar contract this offseason and is (arguably) in his offensive prime.

            2006      2007     2008     2009
G/F         0.66      0.64     0.74     0.50
GO/AO        .93       .97      .99      .73
HR %        4.5       5.2      4.8      6.4
% FB/HR    12.2      14.2     13.3     17.5
RC/G        6.8       8.8      8.5      7.0

Teixeira is an interesting case because his recent resurgence (six homers in the club’s last 12 games) has propped up an incredibly dismal start to 2009, and elevated his home run percentages above the norm. But looking at his three previous seasons we can determine that like Ortiz, Teixeira is at his best when his GO/AO is closer to 1 and his G/F gives a slight edge to the fly ball. In the heat of his slump on May 15, Teixeira’s fly ball percentage had soared nearly 20 points, from 36.5 in 2008 to a staggering 55.6, which plummeted his line drive percentage from 20.8 to 12.2. Hitting coach Kevin Long told reporters that the emphasis has been on turning those numbers back around, and eliminating any undercut swings that result in fly balls. Not surprisingly, Teixeira’s hot week (15-for-45 with 10 extra base-hits) has upped his G/F and helped stabilize his GO/AO to within .23 of his average.

Bartlett, a significantly smaller bat, presents an interesting distinction from Ortiz and Teixeira.

          2006     2007     2008     2009
G/F       0.81     0.83     0.95     0.58
GO/AO     1.12      .93     1.10      .76
HR %      0.5      0.9      0.2      3.7
% FB/HR   1.3      2.5      0.6      9.4
RC/G      5.2      4.6      4.2     10.6

Bartlett’s batting average in the air hovers around .100 and last season’s high .95 G/F and 1.10 GO/AO resulted in career-low power numbers. It makes sense that if a batter hits more of his balls on the ground, as opposed to in the air; he’s not going to be a big home run threat. But be it Bartlett’s emphasis on line-drive hitting or Maddon’s zany vigilance of fly ball stats, the shortstop has stabilized his G/F to 0.63 and his five homers are part of a three-way tie for tops amongst American League shortstops.

Also, on that list is Derek Jeter, who at a 1.58 G/F is one of baseball’s most extreme ground ball hitters. But even Jeter benefits from a more stable G/F, with his top two home run percentages coming in years where his G/F was in the 0.94 range.

So what does all this mean, exactly?

While there is no hard and fast G/F that guarantees a player’s home run potential, the statistic is an essential component for tracking offensive production and monitoring the dynamics of a player’s swing. On average, players hit ground balls on 42.5 percent of batted balls. Although players with exceptionally low ground ball percentages, such as Carlos Pena (28.9), can still be successful home-run hitters their power is increased by stabilizing their G/F, typically within the 0.55- 0.65 range.

During Pena’s comeback year in 2007, he had a 0.58 G/F and 47 home runs, which accounted for 7.5 percent of his at-bats. Raising his fly ball rate the following season, Pena’s 0.45 G/F decreased his home run numbers to 5.1 percent and lowered the production rate of his fly balls turned homers from 22.9 percent to 15.8 percent.

Conversely, a too-high G/F can handcuff power production and result in slap-style hitting similar to Seattle’s ground ball specialist Ichiro Suzuki. Only three hitters in the majors – Hunter Pence, Casey Kotchman and Russell Martin – hit more than ten homers, while hitting more ground balls than fly balls. Of those three, only Pence had real power numbers, eclipsing the 20-home run mark with 25 knocks.

While batting average and RBI are influenced by uncontrolled factors such as the opposing team’s pitching and defense, G/F only takes into account the type of ball hit, to give a stable barometer of offensive progress. When used in conjunction with a player’s specific tendencies at the plate and power potential, G/F can be used to project offensive efficiency, alter mechanics, and protect against the statistically weakest batted ball, the infield fly.