Baseball Savant defines types of batted balls by their launch angles:
- Less than 10 degrees: ground ball
- 10-25 degrees: line drive
- 25-50 degrees: fly ball
Although it could be argued that batted balls launched between 20 and 25 degrees have characteristics of both line drives and fly balls, in that range exit velocity becomes more significant. Let’s stick with the existing definition.
Based on launch angle, batted balls in the sweet spot for homers are by definition fly balls, despite some disagreement on where the sweet spot is. Indirectly confirming this fact is this SB Nation article that wrote there is a negative correlation between line drive rate and HR/FB. Two views of the sweet spot for hitting homers follow:
- The sweet spot for homers is launch angles between 25 and 35 degrees per this Washington Post article.
- The sweet spot for homers is in the 25 to 30 degree range per Nathan, the Illinois physicist referred to in this Philadelphia Inquirer article.
Regardless of who is correct on the sweet spot, by definition line drives are outside the sweet spot for hitting homers. Therefore, based on logic, when hitting line drives it makes sense that horizontal speed (which reduces time for fielders to react) is more important than distance that the ball travels before hitting the ground. That difference means that for line drives it becomes imperative to center the bat on the baseball rather than hitting the baseball “slightly below its’ equator”(quote from the Philadelphia Inquirer article referenced above) to get the most distance on a fly ball.
Nevertheless, centering the bat on the baseball is only one of many aspects of a batter’s swing that impact exit velocity. When the batters swing is mastered, and if contact with the ball is made in a position that allows powerful contact, then for line drives it’s imperative that the bat is centered on the ball.
Why would a batter want to hit a line drive when it means less homers? Two possible reasons are the batter lacks power to hit homers or the batter wants a much higher percentage of hits. Let’s look at Diamondback batters to see if line drives resulted in a higher percentage of hits.
Insights from Diamondback Batters.
Let’s look at 12 Diamondbacks position players who will likely continue to play for the Diamondbacks next season. During the season the Diamondbacks changed their hitting coaches, so for consistency let’s look at data after the All Star break.
The following table shows solid contact of line drives (LDs) had a higher hit percent (hit %) for Ahmed, Ellis, McCarthy, Peralta, Rojas, and Varsho. The green numbers showed hit % exceeded 80%. That solid contact resulted in a higher exit velocity, making the batted ball more likely to be a hit.
For the entire season, Josh Rojas’ 27.6% line drive percent led the Diamondbacks per Baseball Reference (minimum of 60 PAs). Bill James wrote that it’s relatively rare for batters to hit a higher percentage of line drives than 22%. As a measure of how rare, from 17 July to 3 October Josh Rojas’ percentage of line drives per AB ranked 68th in Majors (minimum of 50 PAs). The significance of his line drive percentage cannot be overstated.
Almost everybody hits 19 to 22% line drives. — Bill James, 2009
The following table shows that the hit % for LDs was greater than for fly balls (FBs). The following table shows clearly that for these Diamondbacks batters, LDs were better outcomes than FBs, even considering the home run per fly ball (HR/FB) rate, which was not enough to make up for the difference in % hits. Nevertheless, if it is a 1-run game and it takes a homer to tie, then it may (or may not) be best to attempt to hit a fly ball homer. My view is that patience usually wins out, so even then LDs are best. The one exception was Jake McCarthy, whose homers make fly balls preferred to line drives (but it’s a close call).
Does it make a difference what direction that the line drive is launched? The following table shows that most of the Diamondbacks had better hit % when their line drives were to the opposite field or to the center of the field. The two batters who did well with pulled LDs were Ahmed and Perdomo. Josh Rojas’ hit % was about the same in all directions.
This SB Nation fan post article showed that for pulled batted balls SLG for FBs was greater than SLG for LDs. The following table shows that it was true for the Diamondback batters, too. The two exceptions were Ahmed and Perdomo.
Therefore, two reasons for Diamondbacks not to pull line drives follow.
1. The SB Nation fan post article referenced above had a graph that showed for pulled balls, an outfield fly ball nearly as good as a line drive for batting average, and an outfield fly ball was better as far as slugging. Therefore for pulled batted balls, a fly ball is a preferred outcome.
2. The Diamondback batters had a higher hit % for center and opposite field line drives, except for Nick Ahmed and Geraldo Perdomo.
Impact of balls with lighter cores.
Last season, two types of baseballs were supplied to teams. Although both types of baseballs were within specs, one had a core weight between 123 and 126 grams, while the other had a core weight between 126 and 129 grams per this MLB Trade Rumors article. The lighter ones have been called “deader” and likely that makes fly ball distances shorter and makes it harder to hit homers.
Did the mix of unchanged and changed baseball have an impact? Seven of the 12 Diamondbacks played in the Majors in 2019. Let’s compare their home runs per plate appearance (HR/PA) for 2019 and 2021. The following table shows that six of the seven had a drop in HR/PA.
Next season, instead of a mix, only the lighter core baseballs will be supplied to teams. Because the changed baseball was likely a significant factor in the drop in HR/PA, switching from fly balls to line drives could increase success.
The approach to hitting line drives is different than fly balls, with successful line drives having a higher percentage of hits and fly balls having a higher percentage of homers. With rare exceptions, batters who hit line drives have best results when they make solid contact, and when they hit the ball either to center field or toward the opposite field. Historically, when pulling the ball, outfield flys are better than line drives.
Next season with all baseballs having lighter cores, line drives will likely provide better results than fly balls (more so than this season).
Most batters hit very similar rates of line drives. Josh Rojas is rare and valuable because he hit a higher percentage of line drives.
I look forward to seeing whether the frequency of line drives is impacted by the efforts of Joe Mather, the new Diamondback hitting coach.