For years -- decades, really -- we've been having the same discussion about how to measure defense. Is it most important simply that the play is made? Or that the play looks good while it happens? We know which one is more exciting, certainly. But which one matters more? Should two players making an out on the same opportunity be given different credit because one made it look easy, and the other one made it look spectacular?
Neither answer is right nor wrong. There's undeniably incredible entertainment value in making a fantastic diving play that leaves the stadium buzzing, even if the dive wasn't "needed." There's also baseball value in crediting the fielder who got there easily. You can do both. That's the beauty of all this, that everyone is welcome to enjoy the game as they may please.
Still, it's a question that has come up often around the Statcast™ lab since the introduction of our outfield range metric, Catch Probability, which takes the inputs of "how far did the fielder have to go?" "how much time did he have to get there?" and more recently "what direction was he going?" and compares that to similar plays to show how often a ball was caught. A play with a Catch Probability below 10 percent is virtually never caught; an opportunity above 90 percent is virtually always caught. For the moment, it doesn't account for home run robberies at the wall.
As you might expect, every time a great diving catch is made, the question is whether the data says that no one else could have made it. Sometimes, that's true -- when Billy Hamilton made one of his patented unbelievable catches to rob Cedric Hunter last year, he did so on an opportunity that had a mere 4 percent Catch Probability. But it's not always true, is it? Let's show you a few examples of how very similar opportunities can look very different, and explain why.
We'll start on May 6 in New York, when Curtis Granderson raced in to make a sliding catch of a sinking liner off the bat of Miami's Adeiny Hechavarria. It looked nice; it was nice. After all, Granderson is 36 years old, and due to the composition of the Mets' roster, he's been forced into center field more than anyone would like. All things considered, he's performed reasonably well there, and he made the play. That's the most important part.

It's easy to understand why people may expect that the Catch Probability on that play was very low, but in reality it was 78 percent. That's simultaneously a nice play and it's also one that's also made more often than not. For example, we found a Randal Grichuk play from last year that was nearly identical in every single way, and we mean identical, as you can see in this side-by-side comparison.

Granderson needed to go 41 feet and had 3.45 seconds to get there, coming in to his left. Grichuk had to go 42 feet and had 3.45 seconds to get there, coming in to his left. Granderson's batted ball had an 86.2 mph exit velocity and a 16 degree launch angle; Grichuk's was hit at 86.9 mph with a 16 degree launch angle. Even the direction of their travel was identical to within two degrees.
The one difference? Granderson's sprint speed was 20.8 feet per second, while Grichuk's was 25.4 feet per second. (Read more about "Sprint Speed" here.) Grichuk was faster, he got there more quickly, and didn't need to leave his feet. It doesn't mean that Granderson doesn't get credit for making the play, because he does -- as we said, he got there, and that's most important. It just means he doesn't get extra style points over Grichuk for having to slide. The point is absolutely not to diminish what Granderson did, it's to not discredit Grichuk for getting there quickly. Catch Probability is, at its heart, a speed-based range metric.
Let's take a look at a more recent example, Kevin Pillar doing his best Jim Edmonds impression with a fantastic dive to rob Jose Ramirez earlier this month. Pillar is someone we've highlighted as a defensive superstar in the past, and Statcast™ considered him one of baseball's five best defensive center fielders last year. He's made a career out of insane catches, like when he robbed Carl Crawford last year on a play with a mere 7 percent Catch Probability. Here's what he did to Ramirez:

Incredible, right? It's undeniably one of the most exciting plays of the year. So why wasn't the Catch Probability elite? Because it was pretty easy to find similar plays where the outfielder didn't need to dive. As we've heard ex-Major Leaguers tell us, some diving catches -- though not all, most certainly -- are for effect.
Let's compare Pillar's play to one that Chris Owings made last April to track down a Starling Marte blast, and again, there's plenty of similarities. Pillar had 4.64 seconds to get to a ball 64 feet away, and Owings had 4.62 seconds to get to a ball 63 feet away from him. They had to travel identical directions from their starting points, within two degrees. Unlike the Granderson example, this isn't about speed, because they had nearly identical sprint speed marks of 25 feet per second. Pillar makes it look great. Owings just gets there.

That's in part because Owings made his first move to the ball 0.2 seconds after contact, while Pillar didn't until 0.5 seconds. It's in part because Owings held consistent speed getting there, while the data shows Pillar actually slowed somewhat approximately two seconds before the ball got there before turning the jets on to make the dive. We found similar catches (slightly harder, actually) by Ben Revere and Jacoby Ellsbury from last year, too. Pillar gets credit for the catch made. He just doesn't get extra credit for the dive.
Let's take it a step further and show you three nearly identical fielding opportunities, with three different outcomes. (We did something similar to this last week when praising Odubel Herrera's fantastic fielding this year.) Here we have Kevin Kiermaier making it look easy, Alvin Toles making a fantastic diving catch, and Adam Jones not quite getting there.

How similar? Toles and Kiermaier each had 4.36 seconds of opportunity time to get there, with Toles 82 feet away and Kiermaier 80 feet, so it was slightly harder for Toles. Jones had to go 86 feet, but he also had 4.42 seconds in which to do it. All three of these are Five-Star catch opportunities. While Kiermaier and Toles each neared a very strong 29 feet per second of sprint speed, Jones' 27 feet per second is almost exactly league average on successful outfield catches, which explains why he wasn't able to make the play. Toles made every highlight show, but you might not have noticed Kiermaier's play.
One more? Let's do one more. Earlier this year, Melky Cabrera came in from left field to make a nice diving catch to take a hit away from Ellsbury: 

As nice as that looked, the Catch Probability was 89 percent. Let's show a side by side of Cabrera's catch with one of Jimmy Paredes catching a fly off the bat of Jose Reyes last year, an 87 percent Catch Probability play.

The Catch Probabilities are similar because the inputs are basically identical. Cabrera had to go 69 feet in 4.79 seconds; Paredes had to go 69 feet in 4.70 seconds. In this case, it actually wasn't about speed, because Cabrera was slightly faster. It was about route -- while they both needed 69 feet, Paredes ran 72 feet, but Cabrera ran more than 77 feet.
If anything, this should make us appreciate Hamilton more, because he has a knack for making great-looking catches that are also Catch Probability catches. But we should also appreciate fielders like Herrera, Kiermaier and Jarrod Dyson, stellar defenders who make tough plays look routine. There's value in that. Let's credit them for it, even if it doesn't make the highlight reels.