Many commentators have said something in the last 24 hours (when I originally wrote this) about how Shohei Ohtani's 6-for-6 historic day was the best offensive performance ever. As it happens, I think the arctex fractional R stat is the best way to answer this question. Let me walk through the calculation play by play, calculating ACR, R, and gACW (updated - finally - april 2025) step by step, using the bb-erd tool.

There are some preliminaries. The current ballpark code for Miami is MAR.0. Looking in bwp-tab, the home team win rate is 470 / 994 for end of 2024 or 0.472837022132797. To set up bb-erd properly (OK, this will be a little easier in a future release), I enter: 

> V MAR.0
> Z 0.472837022132797
> T
erv: MAR.0
score difference: -1
Z: -0.2234
> E 0 0
0.4635
> E 0 1
0.2450
> E 0 2
0.0882

Those last 3 numbers are the ERV table values for the R calculation below.

I was going to also calculate his uACW average, but it turns out the Dodgers had clinched, so it's just zero. The game code for this game is MIA202409190.

The first double:

0 out, 0-0, 0p2000, nPNO=2

In bb-erd: 

> 0p2000
0.7072
> We 0 0 0
0.4728
> We 0 2 0
0.3983
So we have:

ACRc += 0.7072

For R, we have

R += 0.7072 + ( 0.4635 - 0.2450 ) * (1/2) = 0.81645

ACWc += log( 1 - 0.3983 ) - log( 1 - 0.4728 ) = 0.132178999038009

The first stolen base:

1 out, 0-0, 3n6110 

> 3n6110
0.4686
> We 1 3 0
0.4255
> We 1 6 0
0.3789

ACRc += 0.4686 * (1/2) = 0.9415

R += 0.4686 * (1/2) = 1.05075

ACWc += ( log( 1 - 0.3789 ) - log( 1 - 0.4255 ) ) * (1/2) = 0.171175000176232

In this case, the factor of (1/2) is because there are two baseruners.

The single:

8 out, 0-1, 3p5221, nPNO=2 

> 3p5221
1.0262
> We 8 3 -1
0.3435
> We 8 5 -2
0.2544

ACRc += 1.0262 = 1.9677

R += 1.0262 + ( 0.0882 - 0 ) * (1/2) = 2.12105

ACWc += log( 1 - 0.2544 ) - log( 1 - 0.3435 ) = 0.298441569804763

The second stolen base:

8 out, 0-2, 5n6220 

> 5n6220
0.1005
> We 8 5 -2
0.2544
> We 8 6 -2
0.2475

ACRc += 0.1005 = 2.0682

R += 0.1005 = 2.22155

ACWc += log( 1 - 0.2475 ) - log( 1 - 0.2544 ) = 0.307653303056412

The double out at third - that makes him 5 for 6 in arctex:

14 out, 1-5, 5p0232, nPNO=1 

> 5p0232
1.5444
> We 14 5 -4
0.1497
> We 15 0 -6
0.1106

ACRc += 1.5444 = 3.6126

R += 1.5444 + ( 0.0882 - 0 ) = 3.85415

ACWc += log( 1 - 0.1106 ) - log( 1 - 0.1497 ) = 0.352611152741261

The first home run:

31 out, 3-7, 2p0112, nPNO=2 

 2p0112
 1.5504
 > We 31 2 -4
 0.0986
 > We 31 0 -6
 0.0739

ACRc += 1.5504 = 5.163

R += 1.5504 + ( 0.2450 - 0.0882 ) * (1/2) = 5.48295

ACWc += log( 1 - 0.0739 ) - log( 1 - 0.0986 ) = 0.379644262660937

The second home run:

38 out, 3-12, 4p0222, nPNO=2 

> 4p0222
1.7077
> We 38 4 -9
0.0360
> We 38 0 -11
0.0304

ACRc += 1.7077 = 6.8707

R += 1.7077 + ( 0.0882 - 0 ) * (1/2) = 7.23475

ACWc += log( 1 - 0.0304 ) - log( 1 - 0.0360 ) = 0.385436583365441

The third home run:

50 out, 3-14, 3p0223, nPNO=9 

> 3p0223
2.6588
> We 50 3 -11
0.0122
> We 50 0 -14
0.0098

ACRc += 2.6588 = 9.5295

R += 2.6588 + ( 0.0882 - 0 ) * (1/9) = 9.90335

ACWc += log( 1 - 0.0098 ) - log( 1 - 0.0122 ) = 0.387863278186239

Finally,

ACRr = ACRc / 6 = 1.58825

ACWr = ACWc / 6 = 0.064643879697707

ACRa = ACRr * PAPG = 6.755929777305955

ACWa = ACWr * 20 = 1.292877593954131

R = 9.90335

The R value is equal to the tabulated one, but the ACWr is listed at 0.054752764954348 which may just be a cumulation of rounding errors, I'm not sure yet.

All that said, at the end of 2024 in the retrosheet database, the highest fractional R value assigned to a player in one game was:

9.9562 for Mark Whiten (whitm001) in game CIN199309072

So Shohei has one superior, and it turns out the only one. What did Whiten of the Cardinals do in that game? First at bat, a two out grand slam. That always helps. A flyout to start an inning, then a 3-run homer with nobody out. Then a third 3-run homer with 2 out, and a 2-run homer with one out just to finish things up. ACRa 8.132 and ACWa 4.147. That's a hell of a game. Third place behind Ohtani is Phil Weintraub of the Giants in 1944 with 9.6072, and then fourth is Anthony Rendon of the Nationals in 2017 with 9.5265.

Incidentally, these are nowhere close to the record in ACW or ACR, as those are averages not totals. That goes to David Bote for a pinch-hit walkoff grand slam in 2018, which was worth 132.857722066 in ACWa, and good for an ACRa of 14.193170574020237. The maximum ACR for a game is hard to determine with the current version of the software, but that's pretty close to it. The maximum possible was 14.684456685878146 in RFK stadium, but no pinch hitters did that. There have been 5 pinch-hit occurrences of the code 7q0224, which is worth 14.329753832534507.

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