The Tale of Two Exit Velocities

PITTSBURGH – In the 5th inning of last night’s game between the Pittsburgh Pirates and the Arizona Diamondbacks, Pirates first baseman Pedro Alvarez hit the 1,000th home run in the history of PNC Park, accounting for Pittsburgh’s only run during a 4-1 loss to Arizona.

Two innings later in his next at-bat, Alvarez followed the home run with an infield single, reaching first base after the ball ricocheted off the foot of D’Back’s relief pitcher Keith Hessler.

In taking a quick glance at the box score, one sees Alvarez ended his night with a home run and a single. But as the videos above show us, there is much more to those batted balls than that.

Beyond the historical implications of Alvarez’s home run, it’s worth noting that the ball had the seventh-highest apex of home runs hit through Aug. 18 of this year, according to the ESPN Home Run Tracker, rising 151 feet before coming to rest in the right field stands.

The ball traveled ‘only’ 359 feet – leaving the bat with an exit velocity of 104 mph – accounting for the shortest of Alvarez’s 19 home runs on the year and falling under the “just enough/lucky” category on the ESPN Home Run Tracker.

If we want to analyze this even further, it’s worth noting the temperature in Pittsburgh at game time yesterday was a sweltering 89 degrees with 90 percent humidity.  As we know from Dr. Alan Nathan, humid air is less dense than dry air for the simple reason that a water molecule weighs less than an air molecule. This, coupled with the 6 mph wind that was blowing out of PNC Park and Alvarez’s extreme apex may have allowed the ball to travel those few extra feet that allowed it to clear the fence for a home run.

When Alvarez stepped to the plate for his next at-bat, the exact opposite occurred in terms of ball flight – but as it applied to exit velocity, things actually improved.

As our eyes will tell us, the ball Alvarez hit off Kessler’s foot was hit very hard – harder in fact than his home run (the exit velocity of the ball leaving the bat was 109 mph). However, in this instance the ball traveled all of 55 feet before hitting the pitchers foot.

The pitch – a 93 mph four-seam fast ball from the left-handed Kessler – was traveling away from the left handed Alvarez as it entered the strike zone…

Pedro Heatmap 1

…whereas the 73 mph curveball from Hellickson that Alvarez hit for the home run was dipping right into Alvarez’s sweet spot that allowed him to lock, load and unleash a ball high and deep into the air.

Pedro Heatmap 2

This is a case once again where a simple look at the heat map doesn’t do justice. Imagine if Alvarez had been thrown a 93 mph four-seam fastball in the same location he received Hellickson’s 73 mph curveball and vice versa – different results would most likely occur on both.

Ultimately, a little luck was required on both batted balls – one possibly weather aided, the other a product of the field of play – to turn each into hits. However, both balls were hit very hard. So it could also be said Alvarez made his own luck possible.

Either way, as long as Alvarez can keep the batted ball exit velocity 100+ mph on as many balls as possible, he and the Pirates will be happy.¹



  1. Alvarez is batting .622 (23-for-37) when his exit velocity is 100+ mph (through Aug. 18th)