Like most things in baseball, baserunning is a blend of skills and smarts.
It helps to be one of the faster guys in the league, but there are players who provide above average value on the bases despite not having above average speed, as instincts and feel can often make the difference between being safe or out. One of my favorite parts of baserunning is the judgement calls that players are forced to make while running at full speed and expelling all their power and athleticism. In those moments, they have split seconds to weigh the many factors that can impact their chances of getting the extra base.
While basestealing may be the single most exciting part of the game, the decision of whether to try and swipe a bag is much more black and white than other base-running plays. Say you’re a major leaguer leading off first base and are determining whether to attempt to steal second. You already know the catcher’s pop time, and you have a pretty good idea of how long it takes the pitcher to deliver his pitch. You’re also familiar with the pitcher’s pickoff tendencies and footwork, as well as your own speed and ability to time your jump. Yes, maybe you can pick up on a pattern in real time that gives you a slight competitive advantage, or you notice either the pitcher, catcher, or both of them aren’t paying you much attention, allowing you to catch them by surprise. But for the most part, your decision to take off for second is still almost entirely going to come down to how fast all parties involved can boogie.
On the contrary, if you’re at the plate and lace a liner in the gap that splits two outfielders, you’re faced with several different variables that affect your decision outside of just your speed. How quickly do you get out of the box? Are you thinking two right away, meaning you’re running hard and already taking the angle that will allow you to cut the corner of first base and make a good turn that will give you a direct line to second. From there, it’s based on feel and whatever data points you have in your head about the outfielders going for the ball. Which one is going to get there first? Does he have a strong arm? If so, is he accurate? Are his throws any weaker and less accurate if he’s pacing on a diagonal toward the gap and has to plant and throw off his back foot? Or, is the outfielder going to get to the ball quickly and have time to circle it, set his feet, crow-hop, and fire? There are other factors on top of these, too.
Let’s check out a few examples from some of the best base-running plays of the year. I’ll be using Statcast’s Runner Runs metric as a guide for choosing plays. This metric estimates the success rate for each base-running opportunity based on variables such as runner speed, outfielder arm strength, and distance from the given bag. Below, I’ve selected three plays — one at second, one at third, and one at home — that were worth at least .20 runs added. We begin with a hustle double from Bobby Witt Jr.:
Sheesh! Out of the box, this looked like a clear single, even when you consider Witt’s 100th percentile sprint speed. This is a typical line drive to center field, not one that splits two defenders. But Witt knew that in this situation — runners on second and third with one out in the seventh inning and the Royals leading 4-2 — the Tigers might throw to the plate instead of second; he also knew who was playing center field. Riley Greene, an above average left fielder, had shifted shifted over to center earlier in the game, and his skills don’t exactly fit as well there. He has 66th percentile speed and 48th percentile arm strength. On top of that, Greene throws left-handed, meaning that because he was roaming to his right side (toward the left-center gap), he’d either have to take a few steps to line his body up with second (as he did) or plant his feet in the ground and pirouette before getting rid of the ball. In other words, this play is easier for a right-handed thrower. Add up all those factors, and you have a perfect recipe for Witt to take a calculated risk with only one out. If Matt Vierling were still playing center, as he was at the beginning of the game, his speed and righty throwing might have kept Witt at bay. Every single one of these details matters! The next play features Anthony Volpe pushing for a triple on a line drive down the right field line. Volpe has very good, but not elite, speed (28.6 ft/sec, 86th percentile), and because of that he’s a bit more reliant on his decision-making than Witt. On this play, he had a favorable spray angle, but it was going to be bang-bang as long as Jo Adell played it right: 
To me, Volpe seemed to realize that he had a shot at a triple as he rounded first and saw the ball bouncing around off the curved fence in right field. He didn’t have a particularly great turn around the bag, but the slight ricochet gave him enough leeway. Typically, runners should look up at the third base coach once they’re getting to second base, but in this case, Volpe was going three no matter what and kept his head down. Adell delivered a great throw to the cutoff man, but the relay to third was short-hopped, which made it more difficult for the third baseman to field it cleanly and apply the tag before Volpe slid in safely. This is an example of a challenge play, where Volpe put the pressure on the fielders to do everything correctly, and because there were multiple steps that had to be executed perfectly, Volpe liked his odds that one part of the chain would be off by just enough for him to make it. Coincidentally, our final play comes from the same Royals-Tigers series that also featured the Witt double from above. And like that play, the outfielder was Riley Greene. Though this time, the runner was MJ Melendez, who despite his 68th percentile speed has done well on the basepaths this year, with +2 Runner Runs. The play we’re about to watch shows how a runner with just slightly above-average speed can put himself in a position to have above-average outcomes. Here it is: 
Wait a sec, how did he get around to score on a fly ball that seemed likely to be caught? You can’t see it on the broadcast, but Melendez played this exactly right. On a towering fly ball like this one, a runner who begins the play at first should be waiting on second base, ready to pivot in either direction. Once Greene dropped the ball, it was time to take off, and even though the ball landed right at Greene’s feet, there was enough time for Melendez to make it home ahead of the throw. That’s despite the fact that Melendez stumbled on his way around third base; he made up for that because he was in the right place when the ball dropped. Also, remember that Greene doesn’t have a particularly strong arm and was all the way out at the warning track. We could keep going, but by looking at plays at second, third, and home, we now have a better idea of the circumstances that affect base-running decisions. We saw how electrifying speed can manifest plays out of nowhere, but also how sound fundamentals can put runners in a strong position for success. As you’re watching ball for the rest of the summer, pay attention to these types of plays and see if you can pick up on the factors that baserunners must consider when weighing whether to take the extra base. These small details can have a major impact.
