He is a big beefy right-handed pitcher, but perhaps has a little more athleticism that you would expect, (though obviously he isn't Austin Jackson on the mound). I think he provides a little bit of deception in his delivery, but nothing too major, or anything that seems especially hard to repeat.
He faced 4 righties and 2 lefties from the Braves, all MLB caliber or close to MLB caliber players. Here are the results, velocity, and location for all of his pitches in his inning of work.
I don't think his fastball is flat, it moves, and had a little arm-side tail at times. When down it could be a really nice groundball pitch, and could work as a sinker.
It seemed that maybe he wasn't finishing his delivery. He really fell off the mound a couple of times. Just from watching, his release point may not have been real inconsistent, but his body finishing point really was. I would think this would be a little concerning when it comes to injury than control.
The slider did not look impressive for the most part. The break just wasn't very hard, mainly vertical. However, he threw one great one to B.J. Upton that bounced and was chased, only to pull the ball, not land consistently, and yank the next one past the catcher. Rondon also seems to have a separate change that breaks arm-side. He had absolutely no control of this and it moved well off the plate arm-side.
He was obviously hit hard by Justin Upton and Tyler Pastornicky, as both of the flyballs were deep flyballs. The control issues, lack of quality breaking ball, and fastball being hittable are all the problems that Rondon was said to have. Let's look at the data though.
His average pitch was 92.63 MPH. Out of all pitchers that have thrown at least 500 pitches since 2007, that number would be tied for 5th best. The names ahead of him aren't big names (besides Chapman, Cleto was a relatively big name in prospect circles from 2 years ago, and Villarreal is a teammate), but it is clear that Rondon is an extremely hard thrower, with elite velocity. He hits 99-100 MPH, or at least has in other outings, and didn't do so in this one, so one could imagine that it could get even harder.
He threw an average of 96.69 MPH on his fastball. That is tied for Tom Wilhelmsen for the 22nd best since 2007. Rondon averaged 84.5 MPH on his off-speed/breaking pitches. This obviously isn't elite, especially for sliders, and even for a changeup. Speed differential is overrated, but Rondon has it. I would rather him just have a 89-90 MPH breaking ball.
He got 4 swinging strikes, solid for 24 pitches. Amazingly, he got just one called strike. 11 of the 24 pitches were balls, just a 54.2 strike percentage. Obviously this is the problem. The 50 % swing rate is above average though, meaning that even though he threw a lot of balls, he got hitters to swing.
Here is his heatmap (remember, I am not distinguishing between balls and strikes and it is from a catcher perspective:
As mentioned above, it didn't look like he was finishing his delivery, and was throwing mainly arm-side. He threw low and high about equally, usually throwing the fastball high and off-speed low (though sometimes the opposite).
I sort of wonder why Brayan Villarreal isn't getting more talk when it comes to be the Tigers' closer. He throws harder than Rondon (at least his averages are better than Rondon's was in the outing discussed above) and was really successful in the Majors last year. He had the platoon advantage more than league average, but even if he faces more lefties, his numbers should still be solid. For what it is worth, and it isn't worth much because projection systems are terrible at projecting rookie pitchers, Villarreal is projected to do much better.You can see the raw stuff Rondon has. He should be a really nice reliever in the future. Whether or not that future is a month from now is the question. I think Rondon could hold his own and be an above replacement/non embarrassing reliever in the big leagues now. However, I would want to see him get some more seasoning, work on his breaking pitches, and see if he can tinker with his command/delivery a little more before bringing him into high leverage spots on a consistent basis.