Wednesday, September 28, 2022
Statcast: Arm Strength for Fielders
The arm strength leaderboard for fielders is now available on Savant.
If we think about pitchers, their arm strength is easy enough to figure out. While pitches may range in speed from 70 to 100 mph, we know based on the pitch trajectory those that are fastballs, offspeed pitches and breaking pitches. So, we can focus on the fastballs. And those fastballs are also thrown with similar maximum exertion for each pitcher. It's therefore a benign process to simply average every fastball thrown for each pitcher. Jacob deGrom for example has all of his fastballs from 94 to 102 for an average of 99 mph. And this is basically typical that the top-end speed is 3 to 4% higher than the average speed for each pitcher.
When it comes to fielders, we don't know how much they are exerting on each throw. When throws range from 50 to 100 mph for the SAME FIELDER, that is clear evidence. So, we need to select a subset of those throws. But, what subset? The target goal is to have the average throw speed be roughly 5% lower than the fastest throw speed, on a fielder by fielder basis. This will roughly mimic our expectation we learn from pitchers, who throw maximum (or close to it) exertion on every throw.
For outfielders, we find that when we take the 10% hardest throws, and take the average of that, we get results similar to what we find with pitchers. Acuna for example has an average of 97.8 compared to his top end throw of 101.5. His top end is 4% higher than the average. Had we taken his 20% hardest throws, his average would have been much lower than 97.8, and so would not really have represented his "average top end" speed. So, top 10% works, for outfielders. Repeating the same exercise for non-1B infielders, and we find that top 5% satisfies the condition that top end speed is 5% higher than the average speed. And for 1B, who have so many non-competitive throws, we had to select their top 1% fastest throws.
Having done that, we are still in the position that we can't directly compare outfielders to infielders to 1B. Oneil Cruz coming in with the 27th fastest throw in 2022 will tell you that. When you get a running start, then that speed adds to your throw speed. That's how outfielders can get more speed than infielders. We need therefore equivalencies.
How do we do that? Well, we look for players who played both infield and outfield, and compare their average throw speeds. And once we do that, we get a fairly clear pattern. And not only infield v outfield. But also within outfield, we can compare the same players when they are LF, CF, and RF. And in the infield, whether the same players are at 2B, SS, 3B.
Here are the equivalencies, setting RF as the target. When you are at this position, you add that number of mph to get the equivalent speed in RF:
0 RF
+1 CF, LF
+4 SS, 3B
+7 2B
+10 1B
So, a fielder at 90mph at 3B would average 94mph in RF.
What this also lets you do is to compare to any other position. For example, say you wanted to know how each of the speeds compares to what it would be if that player played at 3B. Well, take the above chart, and subtract 4 and you get:
-4 RF
-3 CF, LF
0 SS, 3B
+3 2B
+6 1B
So a fielder that is 85mph at 2B would average 88 at 3B. A fielder that was 90 in CF would average 87 mph at 3B.
Here it is in chart form (click to embiggen). Chart on the left is empirical data. Chart on the right is the proposed best-fit.
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