All doubles are equal, but some are more equal than others

There was a lot of furore about a couple of bizarre plays in this postseason, the one which probably drew the most ire and, therefore the most tweets, was the Kevin Kiermaier’s “rule double” off the hip of Hunter Renfroe.

WHAT IS HAPPENING pic.twitter.com/9dSKcYp20l
— Timothy Burke (@bubbaprog) October 11, 2021

There are many different parts to this which blew it up more than the play below, which happened with Rays fielding back in 2019. It was the postseason, in extra innings, a tied game, two outs and a full count.

How "the stupidest rule by MLB" essentially made this play a ground-rule double rather than error and two bases from where the runners were at:https://t.co/Siercxh5Dw #BlueJays pic.twitter.com/5SOOUbKikq
— Shi Davidi (@ShiDavidi) July 27, 2019

But are fans right to be upset that current rules, unearthed by Jeff Passan, meant that Yandy Diaz wasn’t allowed to score? Let’s find out.

For those asking: Well, Yandy Diaz was halfway between second and third when the ball hit out Hunter Renfroe, so why didn't he get two bases and advance home? Here is the rule from the MLB umpire manual. It has to do with possession — and it determines when the two are awarded. pic.twitter.com/FVXF20QN6Q
— Jeff Passan (@JeffPassan) October 11, 2021

What happens for normal doubles?

Thanks to Baseball Savant, I got the play data for the in-play doubles that happened in the 2021 regular season with a runner on first.

There were 2,351, of which 974 managed to drive in the runner on first, equating to a 41% drive-in rate. Which at the highest level suggests that the special rule and the normal ground double rule are right not to advance the runner on first home. But obviously, there are some scenarios where a runner may be more likely to score than others.

Score on a ball in the gap

A baserunners thought patterns and behaviour are vastly different when there have been two outs than when there isn’t. The runner no longer needs to worry about the hit being caught and them being doubled up, they can run with abandon as soon as the ball is hit. This has a big impact on likelihood of the runner on first scoring.

The likelihood of driving the runner in is nearly doubled with two outs compared to zero or one out. So, for the two situations, fans have some right to be aggrieved by the rules.

Full count forced running

A further common rule of thought for baserunning is that runners should be running with two outs, a full count, and all runners are in a force-out situation. If MLB players are doing this, we should expect to see that the likelihood of scoring from first should be higher than the generic two-out scenario.

There were only 66 doubles on two outs and a full count, but once again, there is a significant increase in likelihood. So, Rays fans had every right to be aggrieved because the rule doesn’t seem fair for their specific circumstance.

Those are the game-situational factors but are there any other ones which could increase the likelihood of the runner on first scoring.

Lightspeed on the basepath

Shocking as it may seem, but there is quite the difference in the speed of MLB players, and you’d think this would impact the likelihood of the runner making it home. Let’s look at it to see if that is the case.

Your league standard speed is around 26.5mph, and that matches up to what we see here, with faster speeds having a higher likelihood of getting home from first. What’s interesting here is that the percentage difference between zero/one/ out and two outs is similar for most speeds, about 26%.

Location, Location, Location

Finally does where the double is hit to make a difference? The answer is yes.

Doubles down the lines are much less likely to drive in the runner than hits to the gaps between the CF and the other OFs. This makes sense as several doubles down the line are softer hit and don’t go as far, making it much harder to score from first.

Model for success

Based on these four factors, you could make a simple model which generates the likelihood of the runner from first scoring. I did, and with the data from Kevin Kiermaier’s hit, it came up with a 93% likelihood of Yandy Diaz scoring.

I don’t think the rule should be based on a model like this, but the question is should the rulebook be so specific to account for the number of outs, the count, the location of the hit, the runner’s speed? I think no to all of them, but I could be brought around to it being adjusted for the number of outs. What do people think?

Russell is Bat Flips and Nerds’ resident analytical genius, and arguably Europe’s finest sabermetrician. If you’re not following Russell on Twitter @REassom then you’re doing baseball wrong.

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