Luis Castillo Lands in Seattle – A Park Factor Analysis

Last Friday, the Mariners made the first big splash of the trade deadline deals when they acquired Reds starting pitcher Luis Castillo. The 29-year-old is enjoying another strong season, having posted a career best ERA so far and his second lowest SIERA. His SwStk% has declined to a career worst though, but his CStr% has risen to a career best to somewhat offset the drop in pure dominance. His GB% has also declined below 50% for the first time since 2018. It seems pretty clear this isn’t exactly the same type of pitcher as he’s been in the past, but he’s been just as effective. Now with the move to Seattle, how might his new park affect his results? Let’s consult the park factors.

Park Basic (5yr) 1B 2B 3B HR SO BB GB FB LD IFFB FIP
Great American Ballpark (Reds) 105 99 102 94 112 104 103 98 100 101 104 104
T-Mobile Park (Mariners) 96 98 93 84 98 103 99 98 101 94 101 98

In the above table, I have highlighted the more pitcher friendly park factor. Before diving into each individual metric, you can see that it’s nearly a clean sweep for T-Mobile in favoring pitchers relative to Great American Ballpark (GABP).

Let’s start with the hit type factors. The two parks are fairly similar when it comes to singles. Both are slightly pitcher friendly, so Castillo shouldn’t be affected much. Singles factor would show up in BABIP, and we find that Castillo has posted a significantly lower mark at home during his career than in away parks. I doubt the park was a big driver of the discrepancy here, but it’s possible his pitching style was just more conducive to preventing singles there.

The big advantage for T-Mobile shows up in the extra-base hit factors. The park is significantly more pitcher friendly for doubles, triples, and home runs. While Castillo has posted a higher HR/FB rate rate at home over his career, he has surprisingly posted an inflated mark in away parks too, though not as inflated as at home. So perhaps for whatever reason, he’s simply prone to allowing home runs on his fly balls, which could stem from command issues, but I am just speculating. The park switch should be a help, but perhaps not as much as the factors would suggest.

What’s interesting is he has allowed a lower ISO at home than away. It’s normal for a pitcher to perform better at home, but given that his home park was quite hitter friendly, this surprises me. I would expect his ISO to improve in his more pitcher friendly home venue, but his issues in away parks makes me wonder how much an improvement he’ll see.

Parks can affect strikeouts and walks too! The parks are fairly similar in strikeout factors, both inflating them marginally. Castillo has posted a meaningfully higher strikeout rate at home, but that could easily be the home field advantage effect, as well as the park factor at work. GABP also inflated walk rate, but once again, we find that he has posted a meaningfully lower walk rate at home. T-Mobile’s walk rate factor is fairly neutral and a bit more pitcher friendly than GABP’s.

Finally, we move on to the two hit type factors where we could clearly identify what’s hitter friendly and what’s pitcher friendly (there’s no good GB and FB factor). T-Mobile suppresses line drives, while it’s less hitter friendly for pop-ups. Both should have a positive effect on BABIP. For once, we see Castilo’s home/away split match the park factor, as he has allowed a higher LD% at home than away.

Overall, we find that the basic five year and FIP factors are significantly more pitcher friendly at T-Mobile than Castillo’s former park, GABP. Though his home/away splits are surprising, it’s difficult to argue that this move, from a strictly home park perspective, isn’t a big positive for his ratios.

Mike Podhorzer is the 2015 Fantasy Sports Writers Association Baseball Writer of the Year. He produces player projections using his own forecasting system and is the author of the eBook Projecting X 2.0: How to Forecast Baseball Player Performance, which teaches you how to project players yourself. His projections helped him win the inaugural 2013 Tout Wars mixed draft league. Follow Mike on Twitter @MikePodhorzer and contact him via email.

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