Top stats to know: Red Sox vs. Cardinals

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Shelby Miller and the St. Louis Cardinals take on the Boston Red Sox on "Wednesday Night Baseball."Joe Kelly and Shelby Miller, who were teammates one week ago, face off this week as opposing starting pitchers on "Wednesday Night Baseball" (8 p.m. ET on ESPN).

Here are the top stats to know about Wednesday’s starters.

Joe Kelly (2-2, 4.37 ERA)

Kelly will make his first start for the Boston Red Sox after being dealt by the St. Louis Cardinals at the trade deadline Thursday. Kelly, a 26-year-old righty, posted a 3.03 ERA in 31 starts from 2012-13 but had an ERA north of 4.0 in seven starts with the Cardinals this season.

Kelly’s struggles in 2014 start with the fastball.

In the two previous seasons, Kelly threw 24 percent of his fastballs up in the zone and allowed a .281 batting average. Thirty-two percent of Kelly’s fastballs have been up in the zone this season, and opponents are teeing off at a .349 clip (MLB average is .273 in 2014). His groundball percentage on fastballs dropped 10 percent as a result.

While the heater has been a problem for Kelly, his curveball continues to improve.

Joe Kelly Curveball, Past Three Seasons

Kelly’s curveball usage has increased in each of the past three seasons. His batting average allowed on curveballs has decreased from a generous .346 in 2012 to a stingy .146 in 2014 (MLB average is .222 in 2014).

Shelby Miller (8-8, 4.14 ERA)

Miller’s ERA is up more than a full run this year compared to last, while his strikeout and walk percentages are heading in the wrong direction.

Shelby Miller, Past Two Seasons

Miller ranked 19th out of 81 qualified starters in strikeout percentage with a below average walk percentage in 2013. Miller’s strikeout percentage ranks 79th out of 95 qualified starters, while his walk percentage is the highest in baseball this season.

Those trends have put Miller in the bottom tier of the league in strikeout-to-walk ratio. Miller's 1.47 strikeout-to-walk ratio is the third-worst in Major League Baseball this season. Only Jarred Cosart (Miami Marlins) and Roberto Hernandez (Philadelphia Phillies) have been worse among 95 qualified starters.