James Shields will make his debut for the Chicago White Sox against the Washington Nationals on Wednesday and the expectation from the White Sox is that he'll step into an immediately useful role in the team's starting rotation.
But in order for Shields to be a successful pitcher, there's a lot he'll have to overcome.
Diminished velocity
Two seasons ago, Shields averaged 92.4 mph with his fastball, but that dipped to 90.9 mph in 2015 and 90.1 mph this season.
As the pitch has declined in speed, it has produced fewer strikes. Two seasons ago, Shields threw his fastball for strikes 65 percent of the time. This season, that's down to 59 percent.
His new catchers
Shields has the lowest called-strike rate of any pitcher in baseball this season (26.6 percent). That is interesting given that he benefited more from his catchers (in San Diego) getting called strikes than the average pitcher in the majors this season. In other words, though Shields wasn't good at throwing strikes, his catchers made him look better with their pitch-framing.
Shields is now on a team with two catchers who have combined to rate the worst in pitch-framing this season: Dioner Navarro and Alex Avila.
White Sox catchers have combined to net their pitchers 137 fewer strikes than the average catcher would have gotten on the same number of pitches. That is by far the worst total in the majors. In other words, if Shields tries to nip the corner of the plate with a pitch, more often than not he won't get a strike call.
This is notable because Shields is walking hitters about twice as often in 2016 as he did in 2014.
Navarro and Avila also struggle to throw out baserunners. White Sox catchers have thrown out 5-of-36 runners attempting to steal, the second-lowest rate in baseball. Opposing baserunners are 8-for-10 stealing against Shields this season.
White Sox's infield defense
Shields goes from a team that had a slightly below average infield defense to one with a significantly below average infield defense.
Padres infielders have converted 73.5 percent of ground balls into outs this season (20th in the majors). White Sox infielders have converted grounders into outs at the fourth-worst rate (70.9 percent).
The Padres infield has accounted for eight defensive runs saved this season (including all plays using a shift). The White Sox defense is 15 runs worse at minus-7.
Shields gets ground balls at a rate (48 percent) that's in line with the average pitcher, so he'll likely be impacted by the defensive decline at least a little bit.
The ballpark
Shields is moving from Petco Park, a home ballpark that is relatively pitcher-friendly, to U.S. Cellular Field, which is hitter-friendly. Right field and right center are about 15 feet shallower in U.S. Cellular, though it's a little deeper in the right field corner than at Petco.
Shields tied for the major-league lead with 33 home runs allowed last season, and has allowed nine through 67 1/3 innings this season.
The league switch
Shields will be trying to make the transition back to the American League, where he won't have the luxury of facing the pitcher once every nine turns (except when he plays in a National League park).
Over the last three seasons, NL starting pitchers have had a 3.91 ERA. AL starters have had a 4.08 ERA.
The gap is actually wider this season: NL starters have a 4.06 ERA and AL starters have a 4.40 ERA.
The projections
Fangraphs.com lists three projections for Shields for the rest of the season. His ERAs in them are 3.82 (ZiPS), 4.11 (Steamer) and 4.39 (Depth Charts).
Based on all the factors noted above, it would seem any improvement would be challenging. But two of the three systems place enough faith in his track record to think he'll buck the many factors likely to work against him.
