The Knuckleball and Home Runs

There’s a sense that the knuckleball is more prone to the home run. The guys on the MLB Network, while watching R.A. Dickey give up three home runs to the Reds, thought out loud that the lack of spin meant that it would go further upon contact and lead to more bombs. The home run seems to be the source of some of the ‘risky’ label attached to pitchers that use the knuckler. Even physics professor Porter Johnson said in a recent interview that if a knuckleball “doesn’t move, it’s basically a home run.”

As with all conventional wisdom, this link is worth unpacking.

First of all, does the population of knuckleball pitchers give up any more home runs than the regular population? On first glance, it’s tempting to say yes — after all, Dennis Springer, Steve Sparks, Tom Candiotti, Tim Wakefield and Phil Niekro have all had seasons in which they gave up more than a homer and a half per game. That’s extreme. Then again, some of them pitched in the homer-happiest of times: the late 90s. In 1996, just to pick a year out of the hat, pitchers gave up 1.64 home runs per nine. In 1917, pitchers game up .04 homers per nine.

If we want to compare Springer’s work with that of, say, Eddie Cicotte, who pitched in the late teens, we’ll have to index each knuckleballer’s seasonal home run rate to the league rate. The resulting number, a HR/9+ if you will, can help us compare knuckleballers to the rest of the league. Using this custom list paired with the league stats on this site, that’s easy enough. We’ll use 70 innings as the cutoff, so that we get the Hoyt Wilhelm closer seasons in there alongside the starters.

The average indexed home run rate for all seasons by knuckleball pitchers is 99.06 (100 is league average). Since 2002, the average home runs per fly ball for knuckleball pitchers is 9.85%, and the league-wide number is between 9 and 10% annually. Your garden variety knuckleball pitcher does not give up more home runs than the league average pitcher.

But are there knuckleballs that are more likely to be hit for home runs? The truism that comes to mind is “If it’s high, let it fly.”

Here’s a graph of R.A. Dickey’s home runs since the 2010 season began, thanks to Joe Lefkowitz’s PITCHf/x site:

You could read this graph a couple ways. In the binary high/low way, it seems to suggest that high knucklers are no more likely to be hit for homers than low ones. After all, of the 48 dots represented on the graph, 24 are at 2.5 feet or higher. But if you look at the strike zone in thirds, you do see that the bottom third has fewer home runs in it than the other two-thirds.

Of course it does. Dave Allen famously graphed the representation of ground balls versus swinging strikes based on placement in the zone:

As you can see, that bottom third of the strikezone (represented by the leftmost space between the two red lines) is where the ground balls live. So, yes, if the knuckleball is high, let it fly, but only because all high pitches are more susceptible to fly balls and therefore home runs.

So what about this spin idea? Maybe high knuckleballs also lack spin — after all, we know spin and movement are intertwined — and are therefore even more likely than a high fastball to end up deposited in the seats?

One thing we probably know for sure is that it’s not the spin itself that’s leading to the home runs. Physics professor Alan Nathan showed in an excellent piece of research that the “spin of a batted baseball is less dependent on the spin of the pitched baseball than previously thought.” In other words, the spin of the baseball coming into the bat does not determine much of the spin on the way out.

But there’s still the possibility that the knuckler with no spin gets hit hard. After all, Dickey has said that he wants a quarter-turn from his knuckleball, so less would be bad. Less spin should mean less movement, which should mean a straighter, possibly higher pitch, and definitely means an easier pitch to hit for a home run. “When it was there, it was filthy,” Dickey said to reporters according to Andrew McCullough at the Star-Ledger following that loss to the Reds. “And when it wasn’t, it kind of tumbled up there.”

So, in other words, a bad knuckleball gets hit for home runs. That’s true of a lot of different types of pitches.