Amed Rosario isn't just the No. 1 prospect in baseball, according to MLBPipeline.com. He's also the fastest shortstop in baseball, according to both your eyes and now the Statcast™ data. Rosario qualified for the Sprint Speed leaderboards after scoring on a Jose Reyes single on Thursday night, and when he did, he entered as one of baseball's five fastest players.
It's not like we didn't already know Rosario was expected to be fast. Over the past two years, Pipeline's reports on Rosario have referred to his "excellent speed" and his "outstanding speed," and when he was promoted, MLB.com's Jonathan Mayo referred to his "plus speed." Speed, constantly, is part of Rosario's package.
"He can change the game with his speed," echoed then-Mets outfielder Jay Bruce on Aug. 4, prior to his trade to Cleveland, to MLB.com's Matt Kelly, "and it looks like he's going to be able to change the game in a lot of ways. I'm excited about it."

Bruce wasn't wrong. As we explained when we introduced Sprint Speed earlier this season, by tracking a player's feet per second in his fastest one-second window, we can get to an extremely satisfying measure of foot speed, with 27 feet per second being the league average, 30 feet per second being elite and the slowest catchers and designated hitters traveling around 23 feet per second. Only the best speedsters in baseball top Rosario, now that he qualifies. 
Fastest players by Sprint Speed in 2017

1. Byron Buxton, Twins -- 30.2 feet per second
   
2. Billy Hamilton, Reds -- 30.1 feet per second
   
3. Bradley Zimmer, Indians -- 29.9 feet per second
   
4. (tie) Dee Gordon, Marlins -- 29.7 feet per second
   
5. (tie) Rosario, Mets -- 29.7 feet per second
   Of course, the bar is a little higher at shortstop, since slow-footed players don't remain there. While the average Sprint Speed across the Majors is 27 feet per second, at shortstop, it's 27.5 feet per second, and entering the season, Trea Turner was the reigning shortstop speed champ. As you already knew by the fact that only three other players at any position topped Rosario, he's the new king of shortstop speed.
   Fastest shortstops by Sprint Speed in 2017
   
6. Rosario, Mets -- 29.7 feet per second
   
7. Turner, Nationals -- 29.2 feet per second
   
8.  Wilmer Difo, Nationals -- 29.0 feet per second
   
9.  Ketel Marte, D-backs -- 28.8 feet per second
   
10. (tie) Dansby Swanson, Braves -- 28.6 feet per second
    
11. (tie) Tim Anderson, White Sox -- 28.6 feet per second
    Remember, anyway, that even though it took a few weeks for Rosario to qualify for the leaderboards, he showed that elite speed basically from the moment he arrived, as he hit triples in two of his first three games. After hitting the second one, on Aug. 3, he took just 11.32 seconds to get from home to third, making it the fastest of any Mets triple tracked since Statcast™ came online in 2015.

Rosario's most recent triple, on Aug. 22, was tracked at 11.33 seconds from home to third, giving him the Mets' top two entries of the past three seasons.
For a player like Rosario, speed matters, and you saw why on Wednesday night, when he hit two relatively weak grounders to slick-fielding Cubs shortstop Javier Baez, with Hit Probability expectations of just 4 percent and 14 percent. Thanks to Sprint Speeds of 30.3 feet per second and 30.8 feet per second, Rosario turned each into a base hit, where slower runners would have likely had two outs.
Speed isn't everything, of course, but it's a lot, especially for a shortstop. The Mets haven't had a ton go right in 2017, but they do have this. Rosario is baseball's fastest shortstop, and given his youth (just 21) and what we know about speed peaking young, it's likely to stay that way for some time.