Which players improved and declined the most in the second half of the season during their careers?

I used Stathead (the data base formerly known as the Baseball Reference Play Index) to find all the players since 1908 who had at least 2,500 PAs in their career in both the first half of the season and the second half.

The cutoff is the All-Star break. That is usually past game 81 and varies from year to year. Not sure how Baseball Reference defines before 1933.

So this means players are not all judged equally here. But this what we have. In fact, there is a pretty wide range in terms of percentage of PAs accumulated in the second half (that discussions comes last).

There were 754 players. 344 had positive differentials, meaning the their OPS in the 2nd half during their careers was higher than in the 1st half. Four players had no differential. 406 had a negative differential. The average was -.004.

Here are the top ten differentials. Ryan Howard stands out quite a bit. 45.5% of his career PAs came in the 2nd half.

Rk	Player	OPS1	OPS2	DIFF
1	Ryan Howard	0.805	0.924	0.119
2	Carlos Pena	0.769	0.858	0.089
3	Lance Johnson	0.676	0.763	0.087
4	Chase Headley	0.705	0.788	0.083
5	Mark Ellis	0.669	0.752	0.083
6	Ryan Zimmerman	0.780	0.862	0.082
7	Eddie Murray	0.799	0.878	0.079
8	Mickey Rivers	0.688	0.763	0.075
9	Adrian Beltre	0.784	0.859	0.075
10	Bill Madlock	0.774	0.846	0.072

Notice that these are all relatively recent players. Here are the bottom ten.

745	Mike Lowell	0.840	0.763	-0.077
746	Willie Jones	0.793	0.714	-0.079
747	Bing Miller	0.864	0.780	-0.084
748	Roger Maris	0.863	0.778	-0.085
749	Ivan Rodriguez	0.835	0.749	-0.086
750	Ryan Klesko	0.910	0.820	-0.090
751	Gus Suhr	0.845	0.751	-0.094
752	Chuck Klein	0.971	0.875	-0.096
753	Darin Erstad	0.786	0.686	-0.100
754	Fred Merkle	0.769	0.666	-0.103

These are not all recent players. Some go pretty far back. No outlier here like Howard.

I also looked at just all the players with 400+ career HRs (57 players).

Rk	Player	OPS1	OPS2	OPSDIFF
1	Eddie Murray	0.799	0.878	0.079
2	Adrian Beltre	0.784	0.859	0.075
3	Carlos Delgado	0.899	0.970	0.071
4	Mark Teixeira	0.845	0.901	0.056
5	Eddie Mathews	0.860	0.912	0.052
6	Mike Schmidt	0.885	0.934	0.049
7	Edwin Encarnacion	0.830	0.878	0.048
8	Duke Snider	0.901	0.940	0.039
9	Barry Bonds	1.034	1.072	0.038
10	Chipper Jones	0.913	0.951	0.038

Now for the biggest negative differentials.

48	Lou Gehrig	1.095	1.067	-0.028
49	Jim Thome	0.969	0.941	-0.028
50	Jimmie Foxx	1.052	1.024	-0.028
51	Mark McGwire	1.001	0.957	-0.044
52	Jose Canseco	0.892	0.837	-0.055
53	Carl Yastrzemski	0.869	0.811	-0.058
54	Adam Dunn	0.882	0.819	-0.063
55	Dave Winfield	0.857	0.792	-0.065
56	Mickey Mantle	1.010	0.941	-0.069
57	Willie Stargell	0.922	0.847	-0.075

Mantle has a reputation for being a carouser. I can't think of any reason why Willie Stargell is first. Now the same two tables for SLG.

Rk	Player	SLG1	SLG2	SLGDIFF
1	Eddie Murray	0.451	0.506	0.055
2	Adrian Beltre	0.454	0.509	0.055
3	Carlos Delgado	0.526	0.573	0.047
4	Mark Teixeira	0.492	0.532	0.040
5	Mike Schmidt	0.511	0.546	0.035
6	Eddie Mathews	0.492	0.527	0.035
7	Vladimir Guerrero	0.538	0.569	0.031
8	Barry Bonds	0.594	0.621	0.027
9	Edwin Encarnacion	0.487	0.514	0.027
10	Albert Pujols	0.537	0.564	0.027

48	Andre Dawson	0.491	0.473	-0.018
49	Jim Thome	0.564	0.542	-0.022
50	Lou Gehrig	0.644	0.622	-0.022
51	Mark McGwire	0.598	0.575	-0.023
52	Jose Canseco	0.534	0.491	-0.043
53	Carl Yastrzemski	0.483	0.439	-0.044
54	Dave Winfield	0.497	0.448	-0.049
55	Adam Dunn	0.513	0.461	-0.052
56	Mickey Mantle	0.584	0.527	-0.057
57	Willie Stargell	0.557	0.493	-0.064

Now, what I mentioned earlier. What percent of PAs were from the 2nd half? Here are the top 10 and bottom 10. The top 10 tended to play awhile back.

Rk	Player	PA2%
1	Luke Appling	56.18%
2	Joe Medwick	55.21%
3	Joe DiMaggio	54.86%
4	Jo-Jo Moore	54.78%
5	Lonnie Smith	54.74%
6	Lonny Frey	54.56%
7	Billy Goodman	54.40%
8	Bill Nicholson	54.35%
9	Dom DiMaggio	54.01%
10	Kiki Cuyler	54.01%

The bottom 10 are mostly more recent. Maybe it has to do with when All-Star games were played.

745	Mark Reynolds	41.13%
746	J.D. Drew	40.97%
747	Barry Larkin	40.96%
748	Jose Guillen	40.95%
749	Prince Fielder	40.92%
750	Jack Clark	40.74%
751	Jay Bruce	40.09%
752	Hanley Ramirez	40.00%
753	Dave Concepcion	39.93%
754	Dustin Pedroia	39.43%

Hank Aaron, Barry Bonds, Aging and Park Effects

This issue came up recently on the SABR list. Is there something unusual about Bonds' performance as he aged? One poster said that both he and Aaron's HR% relative to the league average showed a similar pattern as they aged.  But I think that did not tell the whole story.

So here is what I posted.

Using Baseball Reference, below are the neutralized SLGs by age for Aaron and Bonds. That is adjusted for league average and park effects (and I recall that in AT&T park lefties did not hit very many HRs and that a huge portion were by Bonds himself-more on this below).

Aaron does a bit better in his late thirties than earlier. But his .677 at age 37 is only .025 better than his best year at age 25.

Bonds best year was .854 at age 36. His previous best year was at age 28 with .670. That is .184 higher. His 2nd, 3rd and 4th best years were at ages 37 (.800), 39 (.777), and 38 (.727). So even that .727 was .050 better than anything before age 36.

Aaron's neutralized career SLG thru age 35 was .576. From ages 36-39 it was .591 (for a gain of .015). So, yes, a little unusual to see a player do better at such and advanced baseball age. But nothing compared to the improvement Bonds had.

Bonds' neutralized career SLG thru age 35 was .566. From ages 36-39 it .793. That is a gain of .227. That far surpasses Aaron's gain.

Here are Aaron's stats

20    0.445
21    0.533
22    0.571
23    0.608
24    0.553
25    0.652
26    0.587
27    0.600
28    0.617
29    0.618
30    0.526
31    0.572
32    0.540
33    0.602
34    0.547
35    0.617
36    0.549
37    0.677
38    0.510
39    0.631
40    0.490
41    0.361
42    0.396

Here are Bonds' stats

21    0.416
22    0.479
23    0.515
24    0.447
25    0.577
26    0.526
27    0.647
28    0.670
29    0.637
30    0.567
31    0.604
32    0.567
33    0.599
34    0.591
35    0.659
36    0.854
37    0.800
38    0.727
39    0.777
40    0.667
41    0.514
42    0.535

Using Baseball Reference, here is what I came up with for Bonds' HR% (HR/AB) over 2001-4. Home 13.3% and road 12.2%.

For Aaron over 1970-73. Home 10.5%  and road 6.7%.

Using Bill James Handbooks, here are the HR park factors for left-handed batters in San Francisco

2001-57
2002-55
2003-75
2004-92

Under a 100 means below average (2003-05 was 82). So a number like 57 means the HR% for lefties in SF was 43% below league average.

Using another Bill James book (I think it was called something like the All-Time Source book), here are the HR park factors but for all batters in Atlanta, not just L or R (although my recollection is that Atlanta was symmetrical)

1970-157
1971-152
1972-139
1973-143

157 means that the rate was 57% higher than the league average (not totally sure if those older park factors were for rates or just total HRs).

But in any case, it looks like Aaron got alot more help from his park.

Comparing Koufax's performance change from 1962-3 to the league average change in performance

Something I posted on the SABR list yesterday. The topic was "The myth of the MYTH of KOUFAX."

One thing that gets mentioned here is the strike zone expanded in 1963

How much did this help Koufax? What about the entire league?

Here is the change in some stats going from 1962-63

Koufax
Hits per 9 IP) 6.5-6.2
HR per 9 IP) 0.6-0.5
BB per 9 IP) 2.8-1.7
SO per 9 IP) 10.5-8.9

League
Hits per 9 IP) 9.0-8.3
HR per 9 IP) 0.9-0.8
BB per 9 IP) 3.3-2.8
SO per 9 IP) 5.6-5.9

So he improved in walks alot more than the league average, although he had been improving for some time. Starting with 1958 he had 6.0-5.4-5.1-3.4-2.8. But the drop in 1963 is still very big and it is hard to keep lowering that (unless, perhaps, there is some other big change, like the strike zone).

But he went down quite a bit in SO per 9 IP while the league went up. On HRs, he had about the same improvement as the league. Why would he see such a big improvement in BB rate but a big decline in SO rate?

Koufax fell in BAbip from .268-.241, more than the league, .287-.275

If we do % of batters faced (removing IBBs), we get

Koufax
HR) 1.76%-1.50%
BB) 7.16%-4.24%
SO) 29.2%-25.4%

League
HR) 2.34%-2.02%
BB) 7.79%-6.69%
SO) 14.6%-15.8%

The league improved more on SOs and HRs and Koufax improved more on BBs.

Larry Walker's Road Stats

He is 56th in career WAR for position players.

Walker is 30th in OPS for all players with 2500+ PAs from 1990-2005 in away games (.866). 19 guys had at least .900. Even at 3500+ PAs, he is just 19th. Is that good enough for the Hall?

This link has the data

https://baseball-reference.com/tiny/kqTy0

Walker was 25th in away OPS during 1990-94 (Expos years) for guys with 1000+ PAs with .823. 7 guys had at least .900

One person on Twitter wondered about Hank Greenberg. He was 4th in away OPS using 2500+ PAs over the years 1933-1947.

Some Amazing Stats On Joe DiMaggio On His Birthday; Factoring In How Much Yankee Stadium Might Have Hurt Him Raises His Rank In WAR

These are all posts from a few years ago:

Which Players Had The Best HR-To-Strikeout Ratios? Taking league average and park effects into account, DiMaggio had one of the best HR to strikeout rates ever.

Joe DiMaggio Led MLB In Road Slugging Percentage, 1936-51.

Should Joe DiMaggio's Offensive Value Be Estimated Upwards Because Of Yankee Stadium? If he had normal home/away splits, his numbers would be much more impressive. He would have a career OBP of .413 and a career SLG of .621.

Biggest world series upsets by OPS differential (with this year being 4th)

I used data from Retrosheet and Baseball Reference (the one year missing is 1903 since neither site has OPS allowed for the pennant winners). This is based on regular season OPS differential.

So this year was the 4th biggest upset.

Of course, maybe late season OPS differential could be a factor. But as I recall, there is research that says if a team is hot late in the season it does not necessarily translate into success in the post-season.

But late in the season, the Astros' advantage over the Nats only grew. In the 2nd half Houston had a .222 OPS differential while Washington had .098. In Sept/Oct, those numbers were .276 and .072.

Year	Winner	OPS DIFF	Loser	OPS DIFF	Diff
1906	CHW	0.003	CHC	0.131	-0.128
1969	NYM	0.017	BAL	0.136	-0.119
1921	NYG	0.050	NYY	0.155	-0.105
2019	WSN	0.070	HOU	0.167	-0.097
2006	STL	-0.010	DET	0.052	-0.062
1974	OAK	0.048	LAD	0.109	-0.061
1995	ATL	0.062	CLE	0.121	-0.059
2003	FLA	0.032	NYY	0.089	-0.057
1914	BSN	0.036	PHA	0.09	-0.054
2011	STL	0.049	TEX	0.102	-0.053
1931	STL	0.056	PHA	0.109	-0.053