Simply the percentage of fly balls that go for home runs.

• Not very useful on its own. Typically used to stratify a hitter’s performance.
• Every major league field has different dimensions which change based on what side of the plate the player hits from.
  • Different parks produce different HR / FB ratios

Using high-end physics (i.e. launch angle), baseball forecasters are currently attempting to expand upon this statistic. The graph (above) comes from an article that sums this up nicely: “The Quest to Predict HR/FB Rate” by M. Podhorzer