Cubs, White Sox starters make their pitches

Kyle Hendricks and James Shields will face off on Tuesday Night Baseball at U.S. Cellular Field. Icon Sportswire, Getty Images

The Chicago White Sox host their crosstown rival Chicago Cubs on Tuesday night (7 p.m. ET, ESPN/WatchESPN) in the second game of their four-game season series. Stats & Info looks at the top stats to know on the pitching matchup between Kyle Hendricks and James Shields:

Changeup key to Hendricks' success

Though Jake Arrieta and Jon Lester are thought of as the aces of the Cubs' pitching staff, it's actually Kyle Hendricks who has the lowest ERA in the rotation. His 2.27 ERA ranks third in the majors among qualified starting pitchers, trailing Clayton Kershaw (1.97) and Madison Bumgarner (2.14).

Hendricks is second among qualified starters with a hard-hit rate of 9.3 percent, behind Kershaw (9.1 percent). Hendricks doesn't overpower hitters: He averages 87.5 mph with his fastball, 89th out of 93 qualified starting pitchers, and two of the four pitchers below him are knuckleballers.

Instead it is his changeup that has been a major factor in his success. Opposing hitters are batting .121 in at-bats ending with Hendricks' changeup this season, fifth in the majors (minimum 150 changeups thrown).

Hendricks gets opposing hitters to swing at his changeup 64 percent of the time, the fourth-highest rate in the majors, and to chase his changeup 53 percent of the time, the highest chase rate of any pitch by a qualified starter in the majors this season.

Hendricks has a hard-hit rate of 2.1 percent against his changeup this season (three hard-hit balls allowed), lowest among starters with at least 50 changeups thrown.

In three starts (plus two relief innings) in July, Hendricks has allowed just one run for the Cubs, and it was unearned thanks to an error. Since the National League made earned runs an official stat in 1912, no Cubs pitcher has made four (or more) starts in a calendar month and given up a total of zero earned runs.

Shields getting back on track

James Shields allowed 21 earned runs in 8 2/3 innings in his first three starts with the White Sox, good for a 21.81 ERA. In six starts since, Shields has a 2.52 ERA in 39 1/3 innings, the best ERA in the White Sox rotation over that span.

Shields has gone at least six innings and allowed two or fewer earned runs in each of his last five starts, tied for the second-longest such streak of his career. He can match the longest with another such outing Tuesday.

What has contributed to Shields' turnaround? He has seen much improved results with his fastball.

In his first three starts with the White Sox, opponents hit .500 with a 1.535 OPS in at-bats ending with his fastball. Since then, opponents are hitting .172 with a .560 OPS in at-bats ending with the pitch.

In particular, his fastball has improved against lefties, who are 1-for-23 (.043 BA) in at-bats ending with the pitch in his last six starts. He has kept his fastball away, throwing it on the outer third of the plate to lefties 61 percent of the time in that span (45 percent in his first three starts).