Flame-throwing prospect Miguel Sime Jr. has been dominating with a new pitch

Q: What is Miguel Sime Jr.'s new pitch that has impressed scouts?

Miguel Sime Jr. has developed a gyro slider, which has become his most trusted pitch, generating a 76% whiff rate.

Q: How fast does Miguel Sime Jr. throw his fastball?

Miguel Sime Jr. averages 99.2 MPH on his fastball, with some pitches reaching up to 102 MPH.

Q: What are the control issues Miguel Sime Jr. is facing?

Despite his impressive strikeout numbers, Sime has issued 11 walks in 14.2 innings, raising concerns about his control.

Q: Who does Miguel Sime Jr. get compared to in terms of pitching style?

Miguel Sime Jr. has drawn comparisons to Jarlin Susana due to his size and velocity, especially after developing his elite slider.

JUPITER, FLORIDA - MARCH 19, 2026: Miguel Sime Jr. #55 of the Washington Nationals throws a pitch during the second inning of a spring training Spring Breakout game against the St. Louis Cardinals at Roger Dean Chevrolet Stadium on March 19, 2026 in Jupiter, Florida. (Photo by Nick Cammett/Diamond Images via Getty Images) | Diamond Images/Getty Images The Fred Nats had an 11 AM game, which was started by their 18 year old flame-thrower Miguel Sime Jr. He has had some impressive outings this season, but this one was probably his best. The powerful right hander was pounding the zone today, throwing 44 of his 62 pitches for strikes in his 3.2 inning outing. In this outing, Sime struck out 9 batters, while walking nobody. That control piece is big for Sime, as that is his biggest area for improvement. It seems like Sime has his command in about half of his outings. In his three best outings, Sime walked one, one and zero batters. However, in his other two outings, he walked six and three batters. When Sime is on, like he was today, he is way too good for Low-A hitters. He was known for his 100 MPH fastball when he was drafted, but Sime developed another weapon that might be even better. In his pre-season scouting report, he did not have a slider as a pitch that was graded. However, MLB Pipeline mentioned that he was “toying with a gyro slider”. That slider he was toying with has now become his best pitch. Based on data I saw on Lance Brozdowski’s substack, heading into this game, Sime was throwing his slider 50% of the time and it generated a 76% whiff rate. That is the highest of any slider thrown at least 55 times that season, not too bad for a pitch he was just toying with this spring. The slider has become Sime’s most trusted pitch, despite the fact he is averaging 99.2 MPH on his fastball. It seems like he has a better feel for the slider than his fastball right now. However, both are massive weapons for him. Sime also mixes in a low to mid 80’s curveball to round out his arsenal. In an interview, Sime discussed how he has developed his slider. He mentioned that it was a pitch that he was working on with his personal pitching coaches, but that it got even better this spring while working with the Nats. Sime talked about using tools like spin axis balls to help refine the shape of his slider. As such a young player, Sime was able to pick things up quickly, and just develop a plus-plus slider overnight. He already drew comparisons to due to his size and velocity. The addition of an elite slider just makes the comparison even more accurate. It is still going to be a long journey for Sime. He is still super young, and strike-throwing is a concern. Even after not walking anybody today, Sime has 11 walks in 14.2 innings so far. However, he also has an insane 32 strikeouts as well. Like Susana, there is reliever risk, but if he is a reliever he can be a dominant one. I knew Sime threw hard when he was drafted, but my first real exposure to seeing him live was at the Spring Breakout game. He was sitting 100 and touching 102 in that outing. We also saw that deadly slider for the first time. Seeing him mow down JJ Wetherholt, who is now having success in the big leagues was crazy. At just 18 years old, he already has big league ready stuff. There still needs to be a lot of refinement, but Sime has plenty of time. He has already shown that he is a quick learner, and with time, I believe he will throw more strikes. It is a high effort delivery, so walks will always be a part of his game. However, his ceiling could be something like a , who can be erratic at times, but has the raw stuff to get away with it. As such an inexperienced pitcher with control questions, Sime will be a slow burn, but we are seeing great progress already. One of the questions about him is what sort of secondary pitches could he develop. Now that question has been answered with the addition of an elite slider. With two elite pitches, he has a pretty clear path to at least being a high leverage reliever. However, if he can find a way to throw some more strikes, Miguel Sime Jr. will be one of the best pitching prospects in baseball. This Sunday, I will actually be down in Fredericksburg. While I am there, I will have the chance to chat with Sime and fellow top pitching prospect Landon Harmon. I am excited to pick their brains, take a look at how they throw their pitches and ask them about their transition to pro ball.