pokey_reese said:
To me the big thing that stood out, and still does, was the complete lack of walks after April/May:
April: 13
May: 12
June: 3
July: 3
August: 6
September: 1
His K numbers were fairly steady over that time, but he just stopped walking entirely for months. Given his bad BABIP numbers during those months, one would think it was the result of pressing and expanding his zone in an attempt to hit anything, but his O-Swing% numbers are just a shade below league average (29.3% vs 31.1%), so it doesn't look like that was the case. Actually, it's almost eerie, but his plate discipline numbers at Fangraphs are almost identical to the ML average across the board.
This may just be a case of a young guy who had so much success in the minors learning that big league pitchers can paint the edges much better, and so he gets caught looking at a lot more called third strikes in some ABs (leading to more Ks) and then swings at more close pitches than he did in the minors in 2-2 and 3-2 counts, reducing the walk rate.
I think you've hit the nail on the head RE: Xander. I think his approach, and the change in his approach over this year, reflects a young player learning the strike zone and then learning to make contact. Here's some brooksbaseball charts:
The first chart shows Xander's criterion at the plate. Criterion is an excellent measure of bias: independent of plate discipline, and for any given pitch does xander prefer to swing or not?
View attachment 580
We can see by this chart that Xander has become more aggressive as the season unfolds over time. Perhaps this is indicative of a player learning the MLB strikezone, in order to develop better contact skills at the plate. If so, then we should expect to see his whiffs per swing reduce over time. Alternatively, it may indicate that the player is pressing, if so then whiffs per swing should increase over time:
View attachment 581
Here we can see that Xander was whiffing the most at the beginning of the season; however, we can also see a quadratic downward trend as the season develops. In other words, as Xander has become more aggressive, he's been able to make contact. This supports the speculation that Xander was learning how to read MLB pitches, and then putting this information into practice through the season by swinging more frequently. It's a small sample size, but it culminates in better contact rates in the last two months of the season so far, which may indicate that Xander has learned to improve his hitting.
I look forward to seeing whether this carries over into next season. If the speculation is accurate, we may see a vastly improved hitter in 2015.
