How base stealing made a (mini) comeback in 2020

I did what I often do when looking for article ideas, which is digging through the leaderboards over at FanGraphs to see if anything catches my eye. I noticed that the number of steals (adjusted for season length) slightly increased in 2020.

It shouldn’t come as much surprise, then, to hear that stolen base attempts were also up last year.

Granted, teams were still considerably more hesitant to steal than they were at the start of the 2010s. To some extent, the home run surge in the back-half of the decade likely contributed to this trend. The higher the home run rate, the greater the relative cost of being thrown out stealing. That stolen bases waned during a power-driven era isn’t overly-shocking. What is intriguing to me, however, is the rise in stolen base success rate.

And if you want all of these graphs consolidated into one table:

Fewer runners tested opposing defenses, but the ones that did were more likely to get away with their thievery.

What can explain this? I don’t think catchers were especially rusty in the unorthodox 2020 season. Their collective fielding percentage, .993, was the exact same as it’s been in seven of the past eight years. I would love to look at Statcast fielding data, namely, pop time, but those catcher metrics don’t appear to be publicly available for 2020. What we can do as a rough proxy is compare 2015 and 2019, since those two seasons have the largest stolen base success rate gap in the Statcast era.

The average pop times for attempts at second and third base are...virtually identical. That would indicate the key factor here isn’t catchers. Using Statcast’s data, we can turn to the runners themselves and take a look at what percentage of steal attempts were at second base vs. third.

There doesn’t appear to be much here. The lowest success rate pairs up with the highest share of second base attempts, but the highest success rate corresponds to the second-highest 2B%.

Another possible explanation is that the success rate rose because better base thieves started comprising a greater share of attempts. This is reflected in the data...sort of. I took the top 10 and 25 leaders in stolen bases attempts and calculated what percentage of the MLB total they made up for that year.

It’s worth noting the top 10 made up a greater share of all attempts in 2020 than in any of the five preceding seasons. At the same time, though, 2016, the second-lowest success rate, had the second-highest top 10 share and the highest top 25 share.

In my mind, that leaves two main theories in play as to why the success rate surpassed 75% last year:

1. Individual season-to-season data still suffers from small sample size shenanigans. In reality, there’s nothing major to see.
2. Teams have gotten smarter with regards to when they steal, which pitchers they steal against, etc.

For now, I guess we can add this to my list of weird things I’ll be watching for in 2021.