The Baseball Cube doesn’t list it. Neither does Baseball Reference nor FanGraphs. If you want to know the ratio of ground balls to fly balls being produced by a minor league pitcher, you have to go to the player pages located at MILB.com or Minor League Splits for what I consider to be the third most important stat in predicting major league success behind strikeout and walk rates. What is so important about GB/FB, you ask? Well, pull up a chair my friend and take a look.
In a study published in The Hardball Times Baseball Annual 2007, Dave Studeman used batted ball information from 2006 to estimate the run values of strikeouts (-0.113), walks (0.30), ground balls (0.045), fly balls (0.192), and line drives (0.391). Studeman concluded that fly balls are more than four times as valuable as ground balls, even though the batting average on ground balls was slightly higher than fly balls. The discrepancy in value derives from the fact that fly balls are more likely to go for extra base hits and ground balls are more likely to produce double plays.
To appreciate the difference between fly balls and ground balls, consider two pitchers who neither walk nor strike out anyone. One pitcher is an extreme fly ball pitcher (i.e. all balls hit into play are fly balls) and the other is an extreme ground ball pitcher (i.e. all balls hit into play are ground balls). Assuming the batting average against for ground ball pitcher is .300 and the fly ball pitcher is .225, the ERA for the ground ball pitcher would be 1.74 and for the fly ball pitcher would be 6.69.
Obviously, there are no pitchers who produce only ground balls, though it is worth noting that there are three times as many ground ball pitchers (i.e. pitchers who produce more ground balls than fly balls) as there are fly ball pitchers among major league starters. To get a more realistic view of how GB/FB affects the ERAs of major league pitchers, the chart below plots expected runs per nine innings using the run values calculated by Studeman. Key assumptions for the chart below are that 18 percent of balls in play are line drives, 8 percent are infield fly balls, and that the batting average against for non-strikeouts is .300:
The difference in ERA between a high strikeout-low walk/ground ball pitcher and a low strikeout-high walk/fly ball pitcher is substantial (3.15 vs. 5.90). Assuming similar walk and GB/FB rates, the difference between a strikeout pitcher (9.0 K/9) and a non-strikeout pitcher (5.0 K/9) is nearly 1.5 runs per game. Assuming similar strikeout and walk rates, the difference between a fly ball pitcher (0.75 GB/FB) and a ground ball pitcher (2.00 GB/FB) is approximately 0.75 runs per game. Assuming similar strikeout and GB/FB rates, the difference between a pitcher with good control (2.0 BB/9) and relatively poor control (4.0 BB/9) is 0.6 runs per game.
Highlighted in gray near the top center of the table is the projected ERA for a solid-average major league starting pitcher (7.0 K/9, 3.0 K/9 and 1.00 GB/FB). The other gray highlighted cells show how pitchers with fewer strikeouts, more walks, and lower GB/FB ratios can produce the same ERA by being better than average in other areas. Perhaps most interesting is the observation that a pitcher with 5.0 K/9 can actually have an above-average ERA by limiting walks and inducing twice as many ground balls as fly balls.
2009 GB/FB, strikeout, and walk rates of Ranger pitchers and prospects. For prospects who have pitched at multiple level, the statistics listed are for the level where they have pitched the most this season:
[ERA* -- Estimated ERA using GB/FB, K/9, and BB/9.]