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Home Runs Allowed and Fastball Velocity

Have you ever wondered if there is any correlation between fastball velocity and how many home runs a pitcher allows? Why do some pitchers have bad ERAs despite great strikeout and walk numbers? I have answers.

Tampa Bay Rays v Cleveland Indians
Drew Smyly is the poster boy for lots of strikeouts, few walks, but a bad ERA. What is ailing him and others like him?
Photo by Jason Miller/Getty Images

If you read my last post on this particular corner of the Internet, you know that I teased some research that I wanted to do. It all started with trying to figure out why Drew Smyly has had so much trouble with his ERA this year, despite elite strikeout and walk numbers. He isn’t the first guy to struggle with this. Brandon McCarthy was in the same boat in his last half-season with the Dbacks. He was pitching to a sub-3.00 xFIP, but couldn’t keep his ERA below 4. Ian Kennedy has been hit by this several seasons. Getting lots of strikeouts and limiting walks is a very good thing and almost always leads to success as a pitcher, but not always. Why does this happen? That was the question I asked myself when looking at Smyly.

My initial answer (also for McCarthy and Kennedy) was their fastball velocities are in the “danger zone”, too low to keep hitters from hitting balls out of the park on mistake pitches. Pitchers with better velocity, in theory, should be better at limiting homers. That’s the idea. Today, I’m going to test that theory with some data.

First, a disclaimer: I do not profess to be the first one to look at this. This has likely been covered by many other writers over the years. Second, I am not a statistician so this isn’t meant to be an in-depth statistical analysis, just a quick look at the data to spot high-level trends.

Ok, so here’s what I did. I took all of the pitchers (RP and SP) that pitched more than 100 innings total between 2010 and 2016 (666 in total, I know that’s an infamous number, but that’s just how it worked out). I pulled their HR/FB ratio (% of fly balls that go over the fence) and HR/9 (home runs allowed per nine innings pitched) and the average velocities of all of their fastballs (sinker, cutter, four seam). I took the highest of all of their fastball velocities and used that for my analysis. The point here is to compare fastball velocity, HR/FB ratio, and HR/9 and see if there is any correlation.

Here’s the big graph of all of the data.

As you can see, it’s kind of a mess. There is a lot of scatter in the data, which kills the linear curve fits (R^2 values are less than 0.1), but the weak trend is still visible, especially in HR/9. As fastball velocity goes up, HR/9 goes down. HR/FB shows the same trend, but it is very minor. An easier way of seeing the effect velocity has on these two variables is in table form.

Here’s a table of different velocity “bins” that I arbitrarily selected. I took the average HR/FB and HR/9 in each velocity bin and put it in the table.

The trend is easier to see now, right? The guys at 87 and below show a slight reduction in HR/FB and HR/9, but that might just be from the smaller number of pitchers in that region or the fact that they might rely more on off-speed stuff if you have that velocity in order to survive. Either way, the general trend is clear. It’s not a 100% guarantee that throwing harder will lead to fewer homers, but it definitely improves your chances.

Guys like Ian Kennedy, Drew Smyly, Josh Tomlin, Mike Fiers, James Shields, and Wei-yen Chen, to name a few, will probably always have a higher HR/9 than other pitchers with more velocity because they all have fastballs in the 90 mph range or less. This is just something else to consider when evaluating pitchers for your fantasy team. It is part of the reason that higher velocity also leads to lower ERAs, in addition to more strikeouts. We all knew velocity was important (it’s why Nate Eovaldi has been given so many chances), but with so few pitchers like Noah Syndergaard around, we all have to use pitchers with lesser velocity and take the extra homers that come along with that.

I should note that there are some guys that can buck this trend. Adam Wainwright, Masahiro Tanaka, Drew Pomeranz, Kenta Maeda, Jaime Garcia, Madison Bumgarner, and Kyle Hendricks are examples this year. It seems that guys that can limit hard hits with their sequencing or movement can suppress home runs, despite 90-mph or lower velocity. These guys are often on lists of the best contact managers in the game, so that is something else to consider.

Lower velocity with contact management skills can overcome the general trend of more moonshots. That makes these guys valuable in fantasy. Look for guys with low average exit velocity allowed (baseballsavant.com) or low Hard%. These guys can succeed, even with lower than average velocity. Until next time, Tschus!