I'd mentioned strength of opposition late in the season as a contributing factor to the White Sox' putrid offense. I neglected to follow-up on this point after 2015 mercifully ended but was reminded of it by an article at Baseball Prospectus this morning.
Basically, opponent RPA+ measures the quality of pitchers (weighted by frequency) a hitter faced. It's also park-adjusted. "RPA" stands for runs per plate appearance and, as you probably guessed, the "+" means it's measured relative to league average. 100 is average. Above 100 means the hitter faced "easier" pitchers. Below 100 means the opposite. How much above or below 100 tells you the percentage difference from league average. For example, 105 means a hitter faced pitchers 5% easier than league average. 95 means 5% tougher.
While the pitchers a hitter faces are obviously not random - for example, if you hit in a division with lots of quality starting pitchers you'll probably end the year facing overall tougher pitchers - given the turnover on pitching staffs, season-to-season oppRPA+ can fluctuate quite a bit. In 2014, the White Sox faced roughly average pitching. In 2013, they faced easier pitching.
In 2015, though, they faced tougher pitching. Indeed, when you look at the leaderboard, the White Sox are well-represented (along with other AL Central players). Here's White Sox with at least 200 PA, with overall rank among the 344 qualifiers in parentheses:
- Carlos Sanchez - 95 (4th)
- Adam Eaton - 96 (11th)
- Alexei Ramirez - 96 (12th)
- Adam LaRoche - 97 (22nd)
- Avisail Garcia - 97 (27th)
- Jose Abreu - 97 (42nd)
- Melky Cabrera - 97 (47th)
- Tyler Flowers - 97 (53rd)
- Geovany Soto - 98 (70th)
- Gordon Beckham - 98 (72nd)
- Tyler Saladino - 98 (89th)
The story of Sanchez' career so far has been tough pitchers - in 2014, he had a 93, which was also 4th among those with at least 100 PA.
It should be noted that this isn't adjusted for handedness. Switch-hitters like Sanchez and Cabrera should have the platoon advantage every time up. Lefties like Eaton and LaRoche should have the platoon advantage in most PA. And as I've mentioned previously, the White Sox faced fewer left-handed pitchers than league average by a very wide margin. Of course, that also means they faced more righties.
For the newly-acquired players, Dioner Navarro had a 95. Both Alex Avila and Brett Lawrie had a 99.
Reducing the plate appearance threshold to 80 PA, other notables are Trayce Thompson at 96 and Micah Johnson at 103.
And for those wondering how Emilio Bonifacio could possibly get a major league deal after last season, perhaps there's reason to expect a rebound, as he had a 92 - good for 4th toughest.