Barrel Rate
Share of batted balls hit at the speed and angle that become extra-base hits.
What it actually is. The share of a hitter's batted balls struck with a combination of exit velocity and launch angle that historically produces at least a .500 average and a 1.500 slugging percentage. A barrel starts at 98 miles per hour and the qualifying angle band widens as the ball is hit harder.
What a scout reads off it. This is the best public read on power that exists, and it is better than home run totals for predicting next season, because it measures the swing rather than what the wind and the fences did with it. A hitter whose barrel rate jumped and whose home runs did not is a hitter to buy.
Where the lines are. Around 6 to 7 percent is average; 12 percent and up is elite power; the very top of the league lives in the high teens.
Batter's Eye: look up anything in baseball