If you've played organized baseball at some point in your lifetime, you've most likely had a coach that told you to swing the bat with a slight downward hack. After all, the goal of hitting was to create backspin with the theory that more backspin equaled more carry with the ball. I recall reading a story when I was younger that the Twins had their players practice getting backspin on the ball by hitting off a batting tee. Of course tee work is important and according to the article, players like Justin Morneau and Michael Cuddyer were so adept with their swings that they were supposedly capable of hitting home runs off a tee while standing at home plate.
This advice is so ingrained that local journalist Lindsay Guentzel was told that very thing when she competed in TC's softball home run derby in 2013. At the time she was co-hosting a radio show with Ron Coomer and in a short video, Guentzel asked Coomer for hitting advice before the competition. As you likely guessed, Coomer told Guentzel to swing with downward hacks in order to generate backspin. When it was her turn to bat, Guentzel did succeed in knocking one over the fence, though as you might expect TC ended up winning the derby.
So what's the big deal? Well, it turns out that bit of advice is totally wrong.
Now I am aware that players shouldn't "chop wood," so to speak, when swinging at the ball. However, when Guentzel competed at Target Field I didn't know of the change in philosophy at the time. Rather, I was using simple intuition (and some math content that I've used as a teacher) when I left a comment for her suggesting that Coomer's coaching might work in baseball but it was poor advice in softball. In addition to the comment, I even took the time to make some simple diagrams that demonstrated my point. I don't have the originals anymore, but being "simple diagrams" it took me just a couple minutes to remake them. Plus, this time there's a silhouette of a baseball player!
Red is the path of the swing, blue is the path of the ball
Making contact with the ball at the front of your body as you use a downward hack, you've got just one point of intersection so your timing has to be perfect. Oh, and you have to hit the ball at a slightly lower angle than the ball is traveling in order to generate that backspin, just like a tennis player returning a ball to his/her opponent. But if your timing isn't right, you hit a weak grounder, pop it up, foul it back, or even worse - you swing and miss.
If you want to give yourself a better chance of hitting a slowpitched softball, you need to attack it with an uppercut swing. Oh sure, you run the risk of lofting a can-of-corn fly ball to one of the outfielders, but you also give yourself a much better chance of hitting that coveted line drive.
I'd like to point out that the swing angle is exaggerated, but you can see my point here. Though there's still technically just one point of intersection between the ball and bat, there's a much bigger margin of error here (the intersection at the end of the swing is when your bat is pointing towards the pitcher, and if you're swinging at a pitch coming directly at your chest you're either insane or A.J. Pierzynski). If you're early or late with this swing, you're still likely going to make contact with the ball. With the downward hack, your chances of making solid contact drop considerably.
But all of this talk is for softball. What about the baseball swing? Well, the good writers at FanGraphs took care of that already. Eno Sarris - who typically spends more time talking with pitchers - tackled the idea that "chopping wood" is an outdated coaching tip by talking with major league hitters. A couple of the players pointed out that creating extra backspin worked in batting practice, but Sarris also linked to a piece from Alan Nathan that found that it is indeed possible to have too much backspin. Nathan's findings showed that baseballs maxed out their distance in flight at around 1700 to 2000 RPM (revolutions per minute) while there were diminishing returns as the RPM significantly increased over 2000.
If you do some searching on Google, you'll see that the "chopping wood" tip is getting more and more disdain. Even searching on how to create backspin with your swing is met with some resistance as some articles ask if the downward hack is even the best method for success. Bobby Tewksbary - the swing doctor credited with turning Josh Donaldson into a hitting demigod, not former Twins pitcher Bob Tewksbury - acknowledged that the coaching is likely done to correct hand-eye coordination at a young age. This comment by "snowman" in an online forum also points out why the downward swing is taught when honing the batting swing.
I think you'll find near universal agreement -- from Little League coaches through the pros -- that line drives are the best. The disagreement comes in the form of ground balls vs. fly balls. Lots and lots of coaches, particularly at the high school and below levels, believe that ground balls are better. In the majors, the evidence clearly shows that fly balls are more productive (wOBA of .335 for fly balls is way, way better than the wOBA of .220 for ground balls). Now, the lower the level of baseball it is, the more those ground balls will results in errors (say, below high school), so there may be some short term gain from hitting ground balls. But in terms of teaching kids how to play, for me the preference is (1) line drives, (2) fly balls, (3) grounders. And that means a slight uppercut swing path, as Ted Williams pointed out in his book 50 years ago.
In case you're unfamiliar, wOBA (weighted on-base average) is a catch-all offensive statistic that attempts to measure a player's offensive contributions by properly weighting singles, doubles, triples, home runs, walks, etc. You don't need to fully understand it for the purpose here, you just need to know that the wOBA for fly balls is higher than the wOBA for grounders, which makes sense because it's far easier to rack up extra-base hits when hitting the ball in the air rather than keeping it on the ground. However, as snowman said, that wasn't usually taught at the lower levels of baseball. Personally, I know being a relatively faster kid growing up that I was told to keep the ball on the ground and try to create some havoc with the infielders. At that age level, it was an effective strategy. However, as I got older, the infielders got better and the on-field chaos started to dissipate. Well, I also simply lacked the talent to succeed.
Perhaps the best way to demonstrate the advantage of the upward swing is by using some more visuals.
Once again, you see that there's just one point of intersection for ball and bat. As mentioned before with the softball swing, you have to get your timing just right or your solid contact will suffer.
Ah, here is the Holy Grail of coaching a swing. Look at how much the ball and bat overlap in the strike zone. When you hear someone say "he keeps his bat in the strike zone for a long time" or anything similar to that, this is exactly what is being mentioned. The batter is able to make contact at multiple points and a mistake in timing is minimized as a result.
All of this is information I wish I had as a kid but now I look to utilize as a future coach. The downward swing may be beneficial for young kids, but it teaches bad habits that start to manifest at the high school level. We're not making lumberjacks, we're making baseball players.