Despite pitching in the National League since 2011, Matt Garza is no stranger to the DH. Between 2006 and 2010, he pitched for both the Twins and the Rays.
Taking a quick look at his numbers, it’s clear that he favors pitching in the NL. He posted his best ERA (3.32), WAR (4.9), K/9 (8.95), Home Run Rate (0.64), and FIP (2.95) in 2011 as a member of the Cubs. In 5 American League seasons, he has posted ERAs of 5.76, 3.69, 3.70, 3.95, and 3.91. In 3 National League seasons, he has posted ERAs of 3.32, 3.91, and 3.17, despite being a very similar pitcher in terms of walks and strikeouts.
More striking are his sabermetric league splits. In the American League, he never posted a FIP or xFIP better than 4.14. In the National League, he has posted numbers below that consistently, including a 2.95/3.19 FIP/xFIP mark in 2011. So far this season, he has a 3.17 ERA, 3.78 FIP, and 3.85 xFIP.
It also must be considered that he’s going to a better offensive division as well as a more hitter friendly park. The vast improvement from the Cubs’ offense to the Rangers’ should get him more wins, but his ERA, FIP, xFIP, HR/9, K/9, and WHIP will probably all worsen considerably. If I had to guess, in his final 12 (or so) starts, he will post a W/L around 6-4, but with an ERA of around 4.20, as well as increased homers allowed and a lower K/9.
He projects to be a good, but not great, starter for Texas for the remainder of the season.