The 22-year-old Glasnow has been pitching at Triple-A Indianapolis this season and is rated as a consensus top 15 prospect from MLB.com, Baseball America, and Baseball Prospectus.
MLB.com was the highest (relatively speaking) on Glasnow, ranking him No. 10 when 2016 started. With promotions of other top prospects, Glasnow is the league's eighth-best prospect, receiving a sparkling scouting report.
His stuff is ready to get big league hitters out, starting with a mid-to-upper-90s fastball that gets swings and misses both in and out of the strike zone. When Glasnow returned from an ankle injury in 2015, his feel for his curveball was inconsistent, forcing him to throw his changeup more and helping him improve his third offering. Control has always been his biggest issue, but he's made significant strides in that area. Glasnow has a clean delivery and arm stroke, but at 6-foot-8, there are a lot of long parts, making it hard to consistently be on time to the plate, particularly with that breaking ball.
In 96 innings pitched over 17 starts, Glasnow has a 1.78 ERA and a 7-2 record. He has a 113 to 52 strikeout-to-walk ratio, highlighting some of his aforementioned control issues, but he compensated for this by allowing just 57 hits. Overall, he posted a 1.135 WHIP.
Glasnow was a 5th round pick by the Pirates in 2011 out of a California High School and jumped into top prospect status just two years later. Pirates fans have been clamoring for Glasnow to come to the Majors for years, especially during playoff pushes, but this promotion comes to fill a need more than anything else.
Gerrit Cole (triceps), Jon Niese (knee, but is expected to make his next start) and Ryan Vogelsong (eye) are all injured. The Pirates called up fellow top prospect Jameson Taillon to help with this problem but now he is on the disabled list with shoulder fatigue. In the end, they needed to go to Glasnow, even if he might not be completely ready for the Majors just yet.
As a whole, the Pirates' starting pitching staff has posted a collective 2.1 fWAR this season, ranking third-worst in the Major Leagues. However, their ERA as a whole is slightly better, as a 4.67 mark ranks 11th-highest in the Majors.
Glasnow's MLB debut will come against the division-rival St. Louis Cardinals and Adam Wainwright, as the Pirates look to remain in the mix for a Wild Card spot.