Relevance of First and Second Half Stats

Coming into the 2014 season, Jean Segura’s 2013 production still baffles me (I have two more pieces on him coming up in the future). He had a an amazing first half (11 HR, 27 SB, .325 AVG) and then his production dropped off in the second half (1 HR, 17 SB, .241 AVG) which no obvious signs of change. Other players showed the same decline like Chris Davis (.461 wOBA to .365) and Jason Kipnis (.387 wOBA to .317).  Players exist on the other end of the spectrum. They seemed to get better in the second half of the season. Elvis Andrus went from hitting .242 with no home runs to .313 with four dingers.

Having more data is always better. Using three to fours years worth of data make the best projections. It is just human nature to remember the most recent results and quickly react off of them. Whether it is fantasy baseball or the economy, people jump immediately to action. I will look at probably the smallest set of data (besides pitch velocity) which fantasy expects use: half season data.

I will start with the easy answer: No, first and second half stats are not as important the entire season for pitchers and hitters.

If you have a real life and want to get on reading about the Astros outstanding bullpen, go on. For the two or three others, here is a longer math filled response with a little more grey area.

I took a player’s 1st half (1H) and 2nd half (2H) stats and full season season data. Then I calculated the r-square (a value of 0 means no correlation and a value of 1 is perfect correlation) for the three data sets compared to the next season’s stats. I will start with the hitters who I set a min of 200 PA in each full season.

Season 1 to Season 2 0.195 0.339 0.352 0.504 0.754 0.593 0.136
1H Season 1 to Season 2 0.109 0.237 0.239 0.393 0.680 0.481 0.075
2H Season 1 to Season 2 0.136 0.253 0.266 0.412 0.688 0.520 0.089

The table has two spectrums. On one end is Plate discipline (K% and BB%) which correlates nicely with both full and half season data. BABIP, which barely correlates, is on the other end. All the other other stats are some combination of the two. AVG, which is heavily BABIP driven doesn’t correlate as good as OBP which includes a player’s walk rate.

Here is a look at Kipnis’s and Segura’s 2013 seasons which saw 2H dropoffs. Both of them saw a drop in BABIP with Kipnis’s going from .351 to .326 while Segura’s went from .349 to .285. A decent drop for each hitter. With BABIP taking so long to correlate, it is tough to take much credence in either value. Now looking at the plate discipline stats, Segura had a higher strikeout percentage in the season’s 2nd half.

Kipnis: BB%, K%
1H: 12%, 22%
2H: 11%, 21%

Segura: BB%, K%
1H: 4%, 12%
2H: 4%, 16%

Kipnis barely saw his eye numbers barely improve while Segura saw a decent jump in his strike out rate. While I should use the complete 2014 stats, I would worry more about Segura bouncing back from his 2H troubles because of the increased strikeout rate jump which stabilizes quickly.

AGain, use the yearly stats over 1H or 2H stats, but a person may need to take some credence in 2H plate discipline based stats (K%, BB%).

Now onto the pitchers. For them, I used 40 IP as my cut off point and here are the results.

Season 1 to Season 2 0.158 0.112 0.223 0.549 0.315 0.080 0.030
1H Season 1 to Season 2 0.093 0.063 0.134 0.448 0.235 0.036 0.013
2H Season 1 to Season 2 0.106 0.070 0.176 0.489 0.224 0.056 0.021

Pitcher plate discipline stats, like the ones for hitters, correlate the best with K% being the only one over 0.5 and BB the net highest. Let’s look at two pitchers, R.A. Dickey and David Price in 2013. Both struggled in the 1H and then turned their season around in the 2H.

1H ERA: 4.69
2H ERA: 3.56

1H ERA: 3.94
2H ERA: 2.87

Now here is how they each made their improvement.

Half: K%, BB%, HR/9, BABIP
First: 17%, 9%, 1.4, .260
Second: 22%, 6%, 1.4, 271

Half: K%, BB%, HR/9, BABIP
First: 21%, 4%, 1.0, .322
Second: 20%, 3%, 0.6, .281

Dickey’s 2H improvement is based on plate discipline while Price’s is based on batted ball distribution. People, should use their full season stats to determine their overall value, but I may give Dickey’s late season improvement a bit more credit.

Just remember doing the upcoming fantasy season, people are more likely to remember and act on the last set of data the most which includes first and second half stats. With the exception of plate discipline stats, it is best ignore any first and second half centered data and and instead look at data from a full season or more.

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 twice, and got his first NFBC Main Event win in 2021. Follow him on Twitter @jeffwzimmerman.

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10 years ago

How dare you say I have no life!?! (hurts a lot more when it’s true, so be more careful in those situation-types from now on)