When the Yankees placed Michael Pineda on the disabled list at the end of July, there were still a few days left before the trade deadline and it seemed like the Yankees might trade for a starting pitcher. Instead, Brian Cashman opted to hold onto the young prospects that other teams were coveting, and promoted Luis Severino to take Pineda's spot. The Yankees' offense was boom or bust in August, making some games less fun to watch than others, but Severino continued to pitch well, even when the offense didn't pick him up. Through his first five starts, Severino has excelled, certainly living up to the hype that built up as he worked his way through the minors. How does his performance so far compare to the first months of other young Yankee pitchers?
Through his first five starts, the 21-year-old has pitched 29 innings with a 2.17 ERA and 3.72 FIP. He's notched 29 strikeouts, for a perfect 9.00 K/9, with 3.41 BB/9 and 0.93 HR/9. It would be nice to see that walk rate come down a bit, but he hasn't gotten into huge trouble because of the walks yet. Four of his five starts have been quality starts, and in his last outing he threw six shutout innings against the Braves. Severino pitched so well while Pineda was on the disabled list, that the Yankees had decided to go with a six-man rotation when Pineda returned, allowing Severino to stay in the rotation. Of course, CC Sabathia's DL trip forced the Yankees to nix that idea, but Severino has still shown that he deserves the spot.
Pettitte broke into the majors in the 1995 season as a 22-year-old, though his first few appearances were all out of the bullpen. It wasn't until the end of May that he made his first start with the Yankees, striking out three batters, walking two, and giving up one solo home run through five and one-third innings of work against Oakland. He pitched a complete game during his next outing, giving up three runs in the process. Pettitte held Oakland to just one run for a second time in his third start then got roughed up by Detroit and Cleveland. He gave up three home runs and six earned runs through five and one-third innings against the Indians. Through his first five starts, Pettitte pitched 31.1 innings with a 4.31 ERA. He recorded 17 strikeouts for a K/9 rate of 4.88, 1.91 BB/9 and 1.43 HR/9. Of course, Pettitte went on to experience a successful, lengthy career, spending most of it with the Yankees before finally retiring for real.
Like Pettitte, Kennedy also made his Yankee debut as a 22-year-old when rosters expanded in September. In his first outing, he held the Devil Rays to one run and struck out six through seven innings of work. He held the Royals to just two runs through five innings in his second start. His final start was the best of the bunch as he limited the Blue Jays to just one hit, struck out seven and walked four. He only made three total starts in September, but he pitched well (aside from the walk rate) during that time, especially compared to his 2008 season, even though it's an admittedly small sample size. He ended 2007 with a 1.89 ERA, 3.77 FIP, 7.11 K/9, 4.26 BB/9 and 0.47 HR/9. He failed to build upon his success the following year, though. In 2008, Kennedy walked so many batters that his BB/9 (5.90) was almost higher than his K/9 (6.13). Yikes. He left the Yankees in a trade following the 2009 season and has bounced around from the Diamondbacks to the Padres since.
After being drafted in 2009, Greene finally broke in with the Yankees last season as a 25-year-old. He made his first appearance out of the bullpen and even though he wasn't charged with an earned run (thanks to an error by Derek Jeter) he walked three of the five batters he faced, and three runs scored. Greene was sent back to the minors following the game and stayed there until July when the Yankees traded Vidal Nuno and needed someone to take his spot, since it was a rest day for newly acquired Brandon McCarthy. Since the rotation was perpetually injured, Greene managed to stick in the rotation for the rest of the season. In his very first start, he held the Indians to two runs through six innings. Next he faced a tough Orioles' lineup and struck out nine batters through seven and one-third innings. In his first five starts Greene through 29 total innings with a 3.72 ERA, 7.13 K/9, 1.91 BB/9 and 0.93 HR/9. He looked fantastic throughout the season then was traded to the Tigers as part of the deal that brought the Yankees Didi Gregorius. He got off to a hot start in 2015, which led to much clamoring about the trade, but Greene was eventually demoted to the bullpen, and recently had to undergo hand surgery.
Finally, Wang made his debut at the age of 25 at the end of April, 2005. His first start was against the Blue Jays, and he held them to two runs on six hits through seven innings of work. Nothing too memorable happened through his first five starts, but four of them were quality starts, and he gave the Yankees length. Looking back now, 2005 ended up being one of his best seasons before everything went down hill in 2009. Through his first five starts, Wang pitched 33 innings with a 4.09 ERA, 3.27 K/9, 1.91 BB/9, 0 HR/9. He stuck around the Yankees' rotation for several seasons after that, but suffered some major injuries and put up a 9.64 ERA and 5.38 FIP through 42 innings in his last season with the Yankees in 2009. He's shuffled around to a bunch of minor league teams since then (including the Yankees!), only making it to the majors during the 2011-2013 seasons.
Of all the players on this list, Pettitte went on to experience the most success in his career (though Greene's is just getting started), so hopefully Severino will follow that route too.