As a 20 year old rookie Starlin Castro posted a respectable 5.7% walk rate. There was nothing impressive about it except that it's a 5.7% rate at the age of 20. Walks is a skill that improves throughout a player's career so things looked pretty good. In 2011 at the age of 21 it dropped to 4.9% and now at the age of 22 it's only 2.1%.
Fangraphs includes intentional walks when they calculate BB%, but you really want to know the non-intentional walk rate. I also prefer to include HBP so you could call it NiBB+HBP%. Or call it whatever you want. Below you'll see those numbers for Castro.
Of those 7 IBB in 2010, 6 of them were batting 8th. Castro batted 8th that year in 32 games. Interestingly, he was also hit by a pitcher much more frequently than in the next season. As a result, his BB (NiBB%+HBP%) was 5.6%. That's declined to 4.9% and then 2.8% this season. His NiBB% actually improved ever so slightly in his second season, but he didn't bat 8th that season. He's yet to be intentionally walked this year and has barely shown any ability to take the base on balls.
Castro's batting average and OBP is .291 and .307. Both of those are career lows and the OBP is 40 points lower than his rookie season. He reached base via HBP and NiBB twice as frequently as a rookie. Because of this, his OBP is barely above .300 and there's very little difference between his OBP and average.
His wOBA has dropped to a career low .312 (90 wRC+, also a career low).
That's not entirely because of his low walks. He also has a career low .336 BABIP while he has a career high 18.1% strikeout rate. The BABIP isn't too much lower than the previous two seasons and was due for some regression anyway. The 18.1% K-rate is quite a bit higher than the 14.0% and 13.4% he posted his first two seasons.
We expected regression with his BABIP as said already and it's important to point out that we should expect some regression with his walk and strikeout rates. How much? It's hard to say. The best thing at this point is to look at the projections and ZiPS has him a 4.9% BB%. We can also look at when the sample sizes become more reliable, or rather more indicative of what we might see in the future.
Cutter basically searched for the point at which split-half reliability tests produced a 0.70 correlation or higher. A split-half reliability test involves finding the correlations between partitions of one dataset. For instance, taking all of Burrell’s evenly numbered plate appearances and separating them from the odd ones, and then running correlations on both. When both are very similar, the data becomes more reliable. Though a 1.0 correlation indicated a perfect relationship, 0.70 is usually the ultimate benchmark in statistical studies, especially relative to baseball, when DIPS theory was derived from correlations of lesser strength. Without further delay, here are the results of his article as far as when certain statistics stabilize for individual hitters:50 PA: Swing % 100 PA: Contact Rate 150 PA: Strikeout Rate, Line Drive Rate, Pitches/PA 200 PA: Walk Rate, Groundball Rate, GB/FB 250 PA: Flyball Rate 300 PA: Home Run Rate, HR/FB 500 PA: OBP, SLG, OPS, 1B Rate, Popup Rate 550 PA: ISO
Pizza Cutter looked up to 650 plate appearances and if any stat isn't shown here it never reached the necessary .70 correlation.
We can see from this that it doesn't take very long at all for Swing % to become reliable. The same is true for contact, K, and LD rate as well as pitches per plate appearance. Actually, it doesn't take very long for any of the stats listed above.
Through Saturday's games Castro has had 281 plate appearances so the following stats of his are "more reliable" than what he had done before: Swing%, Contact Rate, K-rate, LD rate, P/PA, BB-rate, GB rate, GB/FB, and FB rate. He's very near the point at which is HR and HR/FB rates are more reliable.
In case you're wondering, here's how Castro has fared this season in each of those stats compared to previous years. I've included stats that become reliable with as many as 300 PA.
Not everything is going in the wrong direction. It's nice to see him hitting more line drives though LD% as a stat has questionable results when it comes to whether it's accurate or not. The GB% and GB/FB are both going in a direction that will allow him to hit more home runs, which he's done (HR%, HR/FB).
That's the good news.
His swing% has consistently increased while his contact % has declined in each of his 3 seasons. The K% is way up this year and the P/PA is down. The walk rate is a huge concern in my opinion. Walks aren't the only way to provide value of course, but they are important. Castro doesn't think they are that important or that it's not that important he works on that skill anyway.
"I don't have to change," he said. "The walks and those kinds of things, they're coming. I try to be more patient, but right now, the pitchers are throwing strikes. That's all I can do, swing the bat. If the pitcher doesn't throw strikes, I don't swing. A lot of guys are (first-pitch hitters), and the hitting coach, he likes that. He said if you know your pitch, swing, even if it's the first pitch."
While there is some truth to what he's saying, that's not exactly what you want to hear. And it's not entirely true. The walks aren't just going to come. The fact he's making less contact and striking out more would normally mean an increase in pitches per plate appearance, but Castro's has gone down. The last remark there is odd too. Obviously you can't take every first pitch or pitchers would just throw it down the middle and get ahead 0-1. However, only 31 batters have seen more 1st pitch strikes than Castro. It's unlikely that he's swinging only at his pitches. It's unlikely he's swinging at only strikes. He definitely can be more selective in any count and it's something he needs to work on. Mostly though, you just hate to read comments like this from a 22-year old ballplayer.
To Castro's credit, it does appear as though he has improved defensively and despite having more caught stealing than all but one player has still been a plus on the bases. Overall, there are some positive trends and some negative ones, but as we can see from his batting line, the negative trends are negatively affecting his ability to be as good at the plate as he was in the previous two seasons. I don't expect him to change his stance or any of that, but I do expect him to work on getting better.