MLB hoped to encourage base stealing with two changes. The base bags were slightly enlarged in size. And pitchers are restricted to two free pick-off throws to hold the runner, with the third throw giving the runner an extra base if it is unsuccessful in achieving an out.
So far, the early season results indicate that MLB is getting what it wanted. Stolen bases are both more prolific and more successful. Stolen bases currently are on pace to exceed last year’s total stolen bases by 12%. Furthermore, the current stolen base success rate is 81% which is higher than last year’s success rate of 75%.
It is possible that the success rate may decline as the defensive teams react by focusing on strategies to suppress the running game. On the other hand, if the stolen base success rate continues to be elevated over the course of the season, offensive teams may decide that they should increase the number of stolen base attempts. Some analysts have compared the rule change to allowing the 3-point shot in basketball. It took a period of time for teams to understand the impact of the shots on the overall level of offense and transition to taking more three-pointers.
Increasing the number of stolen bases is effectively a substitute for increasing extra base hits (as in, converting singles into doubles and doubles into triples). But the most important potential impact of the rule is the change in the stolen base success rate. If the number of stolen bases increase, but the success rate remains the same, the actual impact on wins is likely to be minimal or insignificant.
The success rate is the most significant variable because the run value of a caught stealing is 2.7 times more costly than the run value of a stolen base. Generally, the break-even rate for stolen bases has been roughly 67% - 72%, meaning that stolen base success rates must exceed that percentage in order to produce benefits. So, if the rule change causes the average success rate to increase from 75% to 81%, the potential run value of a stolen base attempt will also increase significantly.
Sabermetric authority Bill James provided a 2020 blog piece on stolen base success rates which describes some historical context for the changes in stolen base usage. Prior to 1920, the American and National Leagues did not maintain systematic records of “caught stealing.” The result was “absolutely insane” rates of base stealing and caught stealing. James estimates that the 1920 Boston Braves “saved” 44 runs allowed because opponents attempted 254 steals with a success rate below 50%. James states:
“ But also, as you probably know, when you observe a thing, you very often change it because you have observed it. Teams prior to 1920 did not KNOW how many baserunners they were losing to failed stolen base attempts. Once they had a statistic which showed how often that happened, they began to understand that it was not really paying off. The number of stolen base attempts dropped off a cliff. “
In addition, home run rates and stolen base rates frequently are inversely related. The more home runs that a team will hit, the more cautious the team will be to steal bases. The increase in home runs over the last 30 or so years has led to a general decrease in stolen bases. MLB hopes that the rule change will change this trend.
Astros and Stolen Base Strategies
The sample size for individual teams at this early stage of the season is too small to reach any conclusions. Keeping this caveat in mind, the Astros currently rank tenth in stolen bases with seven. But this number is so small that the ranking could change significantly in a short period of time. The Astros in 2022 stole 83 bases, ranking 16th in the majors. The Astros’ stolen base success rate for both this year and 2022 is an identical 77%.
A few days ago, Tango’s sabermetric blog discussed the performance with the new stolen base rule. Not surprisingly, the results are highly related to the speed of the base runners. Runners with elite speed (more than 30 feet/sec.) are three times as successful as runners with speeds of 29 - 29.99 feet/sec. And those 29 feet/sec. runners are 1.6 times as successful as runners with speed of 28 - 28.99 feet/sec. The runners below 28 feet/sec. speed produce net negative value.
The Astros don’t have any players on the 26 man roster who fall in the elite speed category (more than 30 feet/sec.). Naturally, this will limit the Astros’ ability to achieve top or near top ranking in stolen bases. My recollection is that Jose Siri (traded in August 2022) was the last player to exceed a speed of 30 feet/sec regularly.
The Astros players below fit into the two remaining speed tiers for positive stolen base performance. (Note that these are 2022 Baseball Savant values and therefore exclude the rookie players Yanier Diaz and Cory Julks.)
29 - 29.99 f/s Jeremy Pena
28 - 28.99 f/s Meyers, Hensley, McCormick, Dubon, Altuve
Interestingly, one of the Astros’ leading base stealers last year and so far this year is Kyle Tucker who is listed at 26 f/s. Although averages for this speed are usually associated with negative stolen base value, Tucker is obviously an exception. Presumably, Tucker is particularly adept at reading the pitcher and picking his spots to steal a base.
Tango’s research also finds that the success rate changes in situations involving the first pick-off throw. The base runners who attempt a steal after one pick-off throw are more likely to be successful. Second-pick throws are rare; base runners know this and adjust accordingly after the first pick-off attempt. A steal attempt after the first pick-off throw is equivalent to adding 2.5 feet/sec. to the base runner’s speed. This is a dramatic improvement in the success rate. It means Jeremy Pena would perform like the top of the elite class of runners, and the five Astros in the second tier above would perform at a level close to the elite tier of 30 feet/sec. runners.
If defensive teams react by refusing to make any throws to first base, base runners eventually will figure this out and take bigger leads off first base.
We don’t know if the Astros will change their base-stealing strategy in response to the rule change. But we would expect Pena to be at the forefront of base stealing attempts, followed by the five players in the 28 - 28.99 feet/sec tier. Given his previous success as a base stealer, Kyle Tucker also fits in this category of likely base stealers. Moreover, all of these players should be more inclined to attempt a steal if the pitcher has made a pick-off attempt.
If the Astros increase their emphasis on base stealing, this may affect the decision-making regarding which minor league players will be called up at some point this season. This factor could militate in favor of Pedro Leon, who is probably equal to Pena, if not faster, in speed. Korey Lee and Justin Dirden are two other players with very good sprint speed.
What are your thoughts? Do you want to see more or less emphasis on stolen bases?