With AAA Pitch Clock, Stolen Base Major League Adjustment

On this past weekend’s On The Wire Podcast, there was a discussion surrounding Esteury Ruiz stolen base numbers and the effect of the minor league pitch clock. The gist of the situation can be taken from this Tucker Davidson tweet thread.

The rate of stolen bases is up in the minors as soon as they implemented the change. With the numbers up, I wanted to calculate a simple rule to see how much I should expect a hitter’s stolen base rate to change once promoted, especially rabbits like Ruiz.

For the calculations, needed to set some ground rules. I limited my sample to this season’s hitters who stole four or more bases in AAA. Additionally, they had to go on and have 30 MLB plate appearances. In the end, 40 players met the requirements. I know the sample isn’t the biggest, but I’m just looking at how a hitter’s stolen base rates should change.

For the first test, I compared the stolen base attempt rate ((SB+CS)/(1B+BB+HBP)) in AAA and the majors. In AAA, the median stolen base rate among these guys was 19.5% and it dropped to 10.8% in the majors. When comparing the ratio change (MLB rate/AAA rate) it worked out to 53.5%. So a hitter’s stolen base rate should drop about 50%.

The next test was to look at the success rate. In AAA, this group had an 80.2% success rate and it dropped to 72.1% in the majors. A success of 80% would help a team while 72% hurts their chances of winning.

One final test, what was stolen base per plate appearance change. This value is a quick rule of thumb that takes into account attempts, success, and changes in on-base rate. This value works that the MLB rate is 43% of the AAA numbers.

So going back to Ruiz, here are his expected stolen base rates knowing what he did in AAA.

Esteury Ruiz’s AAA to MLB Stolen Base Rates
SB Stats AAA MLB Estimate
SB Rate 50% 27%
Success Rate 85% 77%
SB/PA 16.2% 7.0%
SB/600PA 97 42

Here are the stolen base per 600 PA values for our projection systems.

Esteury Ruiz’s Stolen Base Projection Rates
Projection SB/600
ZiPS 35
Steamer 40

His projections are close but just a little lower than the value I found. Maybe I should just follow the projections.

Jeff, one of the authors of the fantasy baseball guide,The Process, writes for RotoGraphs, The Hardball Times, Rotowire, Baseball America, and BaseballHQ. He has been nominated for two SABR Analytics Research Award for Contemporary Analysis and won it in 2013 in tandem with Bill Petti. He has won four FSWA Awards including on for his Mining the News series. He's won Tout Wars three times, LABR once, and got his first NFBC Main Event win in 2021. Follow him on Twitter @jeffwzimmerman.

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1 month ago

Does this mean Bubba Thompsons SB success was essentially inflated and less likely to be at play in MLB?

1 month ago
Reply to  Crazyhurdlers

Sic semper lepores!

1 month ago
Reply to  Crazyhurdlers

Not being able to steal first base will clearly be his biggest issue, incredibly small sample but the bat doesn’t look MLB-caliber at all. Bat to ball skills and eye both look very poor.

That said, both the eye test and statcast agree, he’s absolutely rapid. He’s played 7 games and has already registered a 30 ft/s sprint speed and 5 bolts (from 8 competitive runs). Trea Turner leads the league in total # of bolts with 91 from 185 competitive runs. Bubba can run, the steals will be there for as long as they let him flail at the plate.