Regression to mean vs Aging Curve

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TheoSqua
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Regression to mean vs Aging Curve

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A large part of the season's success hinges upon two players rebounding to their career norms: Paul Goldschmidt and Matt Carpenter. 
ZIPs doesn't expect much from either, having Goldschmidt pegged at 118 OPS+ and Carp at 11 OPS+. Not the numbers you want to see from hitters expected to anchor your lineup. 

I wanted to see what Baseball Reference's comparable players looked like and if any of them had a dip in OPS+ similar to Goldschmidt's last season and if they were able to recover:
Hal Trosky - dipped at age 31 and was out of baseball at 33.
Danny Tartabull - dipped below 120 ops+ at age 31 and never rebounded.Wally Berger - no noticeable dip until he retired.
Kevin Mitchell - not comparable.Geoff Jenkins - dipped at age 31 and was out of baseball after age 33. Never rebounded.
Richie Sexson - dipped at age 31 and was out of baseball after age 33. Never rebounded.
Tony Clark - His 30s weren't great. But had a career year in OPS+ at age 33.
Derrek Lee - Manic 30s. Broke his wrist at age 30 and rebounded to have 3 more seasons over 130 OPS+
Fred McGriff - Technically dipped at age 31, had a 142 OPS+ age 35 season. Had a  118 OPS+ in his 32-26 age seasons.
Adrian Gonzalez - Dipped at age 30. 115 OPS+ from ages 32-36. Had two 130 OPS+ seasons at 32/33. Allstar at 33. 
Kent Hrbek - Pretty solid aging curve, no major dip. Out of baseball after 34. 112 OPS+ from 32-34.
Ted Kluszewski - Hit a cliff at age 32. 100 OPS+ from 32-36.Mo Vaughn - dipped at age 31. 112 OPS+ ages 32-35. 
Jeff Bagwell - normal aging curve. 135 OPS+ aged 32 - 36. 

So from 14 comparables the only ones that really excelled in the age groups that Goldschmidt is about to enter are players recovering from injuries or Hall of Fame hitters. 

Oddly enough Adrian Gonzalez might be Goldschmidt's best case scenario. He had a 117 OPS+ age 30 season that drove him out of Boston. After that he had three seasons of 125/130/130 before starting to dive off his cliff at age 34. Derrek Lee was able to recover from a wrist injury to put up a few more solid seasons in his early-to-mid 30s. 

And that's really it. 

Goldschmidt is unique from the rest of the pack because not many hitters had a 30 OPS+ drop in their age 31 season without injury.  The other thing is that Goldschmidt had a rough start to 2018 that was only saved by going on a 1.000+ tear over his last 100 games. So 65% of his last two seasons has been pretty sub-par. 

There are a few reasons to think Goldschmidt might rebound:
- He changed teams, so maybe an additional year to adjust will help him rebound.
- He's going to have the opportunity to rebound. Most of his comparable peers were replaced or not re-signed. Goldschmidt's contract basically guarantees he's going to get full time at bats for another 5 years. 
- Baseball still has to be played. Just because everyone else has aged poorly doesn't mean that has to happen to Goldschmidt. Maybe he ages differently, or adjusts at the plate, or gets on a ridiculous hot streak that breaks his aging curve, steroids become legal, etc..
 
But the odds are his 140+ OPS seasons are over and the team's best case is that he is above average at best and doesn't turn into an albatross. 
I won't go into as much detail with Carpenter, but he also has a lot of reason to think he's not going to become a 140 OPS+ player at age 40. 
Carp is incredibly streaky and all it takes is a bit of salsa for him to disrupt his aging curve more than he has already, so it's not impossible, but not likely. Big jumps in full time seasons from age 31 to 32 like when he went from 120 to 143 are pretty rare from what I can find. Going from 143 to 91 while healthy is also pretty rare. 

Either way, seeing how these two rebound and how the rest of the lineup steps up to fill any gaps the team has at the center of its lineup is definitely something worth watching this season, even if history suggests we shouldn't be too optimistic. 

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