The MLB got a little bit prettier this offseason. Quicker games, more runs, fewer pickoff attempts. You’ve also probably noticed a seemingly big increase in stolen bases. The cause of this uptick has been discussed to painful lengths.
As your local broadcaster may have made abundantly clear, the MLB has implemented a pitch clock! Intended to speed up the game, the clock and limits on pickoff attempts have made it more difficult for catchers to nab base stealers. While the uptick in stolen bases has been obvious to the naked eye, I’ve found myself wondering. By just how much have stolen base attempts and stolen bases increased? How valuable is a stolen base? Who is stealing?
By the Numbers
The first of my questions is certainly the easiest to answer. In 2022, stolen bases were attempted in 5.0% of plate appearances where a stolen base was possible. This year, through Tuesday’s games, that mark has jumped to 6.8%. Accordingly, the league-wide number of steals per game has increased by 39%, from 0.51 in 2022 to 0.71 this season.
The most notable statistical change year-over-year is the increase in the success rate of stolen base attempts. Last year, stolen base attempts were successful at a 75% clip. Now, runners are claiming bases at a 79% rate. New rules have helped to hold the pickoff rate flat at 0.4% on stolen base opportunities despite the uptick in activity on the bases.
So, it’s true; there has been a meaningful increase in stolen bases by most any measure. Our eyes do not deceive us. But how much does it matter?
Assigning Value
Attempting to steal a base is a classic risk-reward proposition. The decision to steal must be made by evaluating a situation. The score, number of outs, where the runners are, etc. It’s never been abundantly clear to me, however, what exactly the risk or the reward is for stealing a base.
RE24 coefficients are a useful tool for determining the expected value of a situation. These values express the average runs a team can expect to score in an inning from each of the 24 baserunner/outs combinations assuming league-average batters and pitchers. According to a 2020 article in High Heat Stats explaining the calculus behind RE24, the RE24 coefficients for a season in which teams average 5 runs per game are as follows:
Roughly approximating these values into 2022’s run-scoring environment, we get the following.
What does this have to do with stolen bases? Let us embark on a mathematical adventure to find out. We can approximate the value of a stolen base in a given situation by subtracting the expected runs before the steal from the expected runs after the steal. For example, the expected runs added from stealing second with a man on first and nobody out would be the RE24 value with a man on second and nobody out (1.089) minus the value of a man on first with nobody out (.868), or 0.22 runs. For brevity’s sake, let’s call this SBr.
Conversely, we can apply the same methodology to the cost of getting caught stealing. This time, we subtract the expected runs pre-steal from the expected runs post-caught stealing. In the same scenario above, that’s .271 (nobody on, one out) minus .868, or -0.60. We’ll call this CSr.
Taking our arithmetic one step further, we can compute the expected runs added from stealing a base based on the league-wide success rate of stealing in a given scenario. That math looks something like this:
Success Rate * SBr + (1 – Success Rate) * CSr = Expected Runs Added
In the above scenario, given this year’s league-wide success rate of 74% on those stolen base attempts, it looks something like this:
.74 * .22 + (1 – .74) * (-0.6) = 0.01
In other words, the league roughly breaks even in this scenario. Another way of looking at the math is to say that if a manager thinks a runner has at least a 73% chance of stealing second with one on and nobody out, he should always give him the green light. (A 2018 Medium article by Jordan Siff takes a look at the breakeven success rate on stolen bases using a similar method.) This is just one of 18 baserunners/outs scenarios that have the potential to yield a stolen base. Rather than drive you, dear reader, completely insane by breaking them all down mathematically, I’ll share the most interesting tidbits I uncovered in examining them all.
According to this method, the most valuable situations in which to steal are with runners on first and second with one or nobody out. Let’s take a closer look at each scenario. Stealing with runners on first and second and one out has obvious benefits; success takes away the potential inning-ending double play and allows the lead runner to score on a sac fly or possibly a ground ball. Success yields 0.43 expected runs and failure yields -0.58, but the league has been successful on a whopping 94% of such attempts this year, for an expected run added of 0.37! The breakeven success rate is a measly 58% in this scenario, yet teams have attempted steals in only 5% of such opportunities.
“Never make the first out at third,” goes the adage. Attempting a double steal with runners on first and second with nobody out is riskier. Getting caught, assuming the runner attempting to steal third is thrown out, reduces expected runs by -0.79. The reward, if successful, is an additional 0.45 expected runs. Last year, the MLB success rate in this scenario was 76%, yielding expected runs added of 0.15. The success rate has skyrocketed this year to 89%, yielding 0.31 expected runs added and a breakeven success rate of 64%.
This year, 83% of all stolen base attempts have been of second base while second base is unoccupied. The weighted average expected runs added of such attempts based on the frequency and success rate of each scenario is just 0.01. Obviously, these situations are far more common than the situations discussed above. But teams only attempt steals in first and second situations at a 3% clip with nobody out and a 5% clip with one out.
Now, there are reasons the game is won on the field and not on paper. Looking at these numbers with no other context would lead you to believe that teams should be stealing every possible chance they get. That would be unwise and isn’t my point. The gaudy success rate on double steals would regress if teams were less selective in when and with whom they stole. But the fact is that there is so, so much room for the success rate to fall before such attempts become a negative expected value proposition. The attempt rates in almost every scenario have ticked up this year, but teams across the league can and should be more aggressive with men on first and second.
Who’s Making Noise
Now that we’ve completed our trip on the Magic Steal Bus, let’s look at some individuals who are exceeding or falling short of expectations in the stolen base department. Ronald Acuña Jr. stands out as the best power/speed threat in fantasy baseball. His 15.0% barrel rate combined with 15 stolen bases to this point in the season is simply unfair. Some more surprising names fit the power/speed bill, like Thairo Estrada and Jorge Mateo, who each have 6 home runs and double-digit stolen bases.
Sitting in third place on the MLB stolen base leaderboard is enigmatic Pirates’ rookie Ji Hwan Bae. He essentially lives off his speed, with 14 steals and 17 runs despite a .202 xWOBA and 19.4% hard contact rate. Jazz Chisholm Jr., unfortunately, fits a similar mold so far this season. He has 13 steals and not much else going his way, with a .265 xwOBA.
Another rookie has, on the other hand, impressed in the batter’s box and on the base paths. Corbin Carroll, the Diamondbacks’ phenom, has used his speed to bolster an already impressive rookie profile. His 10 steals paired with his 31.1% hard contact rate and 10.1% barrel rate will make him a potent threat for years to come in a hitter-friendly home park.
Tommy Edman is off to a slow start on the paths after stealing 30-plus in each of the previous two seasons, tallying only 3 steals through 34 games. He’s seen an uptick in slugging and already has 5 home runs (his career high is 13), but his hard contact rate has dropped well below average, so the power doesn’t seem legit. Randy Arozarena also only has three steals so far this year, but he’s more than made up for it by annihilating the ball.
The stolen bases are here to stay. The implementation of the new rules has been effective in speeding up the game, but they’ve also created more action on the base paths. Fortunately, the increased activity has been accompanied by increased success rates. This observer would love to see teams place more emphasis on getting guys to third base, but, until that happens, let’s enjoy the fireworks.
Photo by Randy Litzinger/Icon Sportswire | Featured Image by Ethan Kaplan (@DJFreddie10 on Twitter and @EthanMKaplanImages on Instagram)
A great read thank you. Reminds me of the Vogelbach commercial (https://youtu.be/ho8SYX9SvX0) on MLB that makes laugh every time I see it.