Is GB rate the same as GB/FB ratio? Do they track together?
On Fangraphs site, it does track together. Let's use Charlie Morton as an example. (Here is the link to Morton's Fangraphs page).
According to Fangraphs, Morton has allowed 204 ground balls, 58 fly balls, and 72 line drives in 2011. His G/F rate is computed by dividing his ground balls by his fly balls (204/58 = 3.52). His ground ball rate is calculated by adding all three of these results and dividing the ground balls by the total number of batted balls (204/334). This gives Morton a ground ball rate of 61.1%.
ESPN's page does this differently. They do not track line drives and only track ground balls and fly balls. Their G/F rate computed by dividing ground balls by fly balls, but most of what Fangraphs classifies as line drives are converted into fly balls. So Morton's ESPN ground ball rate is 221/123 for a G/F rate of 1.80. I'm not sure why ESPN is showing Morton with 10 more balls in play against than Fangraphs, but I'll leave that to someone else to figure out.