HR/FB Rate

HR/FB rate (home run to fly ball rate) is the percentage of a hitter's fly balls that become home runs. MLB average HR/FB rate sits around 11-13% depending on the season and era.

Formula

HR/FB rate = Home runs / Fly balls hit

Line drives and ground balls are excluded. Only batted balls classified as fly balls go into the denominator.

What Drives HR/FB Rate

Three factors primarily determine whether a fly ball clears the fence:

1. Exit velocity: how hard the ball is hit. Exit velocity is the strongest predictor of home run probability. Balls hit 100+ mph have dramatically higher home run rates.
2. Launch angle: the angle off the bat. Fly balls in the 25-35 degree range have the highest home run probability. Too flat and the ball falls in the outfield; too steep and it becomes an easy fly out.
3. Attack angle: the bat angle at contact, which influences both exit velocity and launch angle. A more positive attack angle that matches the pitch plane tends to produce better fly ball outcomes.

Park factors also play a significant role, the same fly ball travels farther in Denver than in San Francisco due to altitude, humidity, and field dimensions.

Volatility

HR/FB rate fluctuates more year-to-year than most hitting statistics. A hitter who posts a 20% HR/FB rate one season may regress toward league average the next without any meaningful change in their skill. This makes it less useful as a standalone projection metric.

For this reason, analysts often look at exit velocity and launch angle data alongside HR/FB rate to distinguish true power skill from variance.

Youth Application

At the youth level, tracking fly ball home run rate is rarely practical. But the underlying concept matters: not all fly balls are equal. A fly ball hit with authority at the right angle is a fundamentally different batted ball than a pop-up or a routine center-field fly out. Teaching hitters to drive the ball rather than just put it in the air reflects the principle behind HR/FB rate.