The Cincinnati Reds top prospect Robert Stephenson has been on a roll lately. Since May 6th he has an ERA of 2.29 in 55.0 innings, but the real run I want to focus on started on May 23rd.
The right hander struggled to start the game, walking four batters and allowing a double while only recording one out. Things changed from that point forward as he struck out the final two batters of the inning. Beginning with that first strikeout, Stephenson has thrown 37.1 innings, allowed just 16 hits, walked just 11 batters and he’s struck out 51 hitters. Opponents are hitting .130 against him in that time frame.
The numbers on the surface are dominant. I wanted to dig deeper, so I downloaded the game pitch-by-pitch data to look at that time frame in terms of the end result of each pitch. Here are the results:
| Ball | CalledK | SwingK | Foul | BIP | |
| 23-May | 17 | 16 | 16 | 13 | 3 |
| 30-May | 31 | 16 | 14 | 22 | 14 |
| 4-Jun | 25 | 15 | 13 | 16 | 18 |
| 9-Jun | 29 | 12 | 18 | 12 | 15 |
| 14-Jun | 48 | 15 | 7 | 11 | 11 |
| 19-Jun | 37 | 15 | 17 | 17 | 14 |
That’s just the raw data and without context it doesn’t do much for us. The stat I was most interested in was the swinging strike rate. Using the Fangraphs leaderboard I sorted the pitchers on their swinging strike rate. Here is the Top 5, and the only five above 13.8% in baseball this season (among starters):
| Pitcher | SwingK |
| Chris Sale | 16.0% |
| Clayton Kershaw | 15.1% |
| Francisco Liriano | 14.4% |
| Max Scherzer | 14.4% |
| James Shields | 14.2% |
Obviously, these guys are getting it done against big leaguers, while Stephenson is only facing guys in Double-A, but at the very least it will give us some perspective.
In this span of time Robert Stephenson has a swinging strike rate of 16.1%. While we are comparing his rate to big leaguer rates, that’s an incredibly high rate of swings and misses.
If we look back up at his game logs, we can see that his start on June 14th wasn’t his best. It easily had the most balls thrown in the game and had half as many swinging strikes as the rest of the games did. In that start, the strikezone was a bit tight, with belt high pitches behind called balls. With that said, Stephenson still didn’t have too much control that night, but it was a little better than the raw numbers suggest.
In the other games we see similar numbers across the board from start to start. If the June 14th start was simply a blip on the radar, we are seeing Robert Stephenson dominate the Southern League much like the best pitchers in the big leagues dominate, if not more so.
With the Reds going out and signing Matt Buschmann to fill out the Louisville rotation over the weekend, it doesn’t seem that the Reds are ready to promote Stephenson to Triple-A just yet, but if he keep doing what he’s been doing over the last month it probably won’t be long until he’s one step away from the big leagues.