From the most recent ask BA:
Is it true that the slider the Mariners won't let Felix Hernandez throw could be his best pitch? That would give him what would appear to be three 70+ pitches on the 20-80 scouting scale, with the makings of a good change and the ability to throw them all for strikes. That seems like it would just be unfair. Will they let him start throwing the slider in the future, or will they encourage him to scrap the pitch altogether to help reduce stress on his arm? Could Felix Fantastico be No. 1 on the 2005 Top 100 Prospects list?
I've heard the same thing. Not many people have seen Hernandez throw his slider, which reportedly has been clocked as high as 91 mph, but those who have say it may be better than his mid-90s fastball and knockout curveball, both of which are plus-plus pitches.
Hernandez has torn up the minors to this point without using the slider. He already may rely a little too much on his other breaking ball, especially with runners in scoring position. The Mariners haven't said if and when they'll let him go to the slider, but why fix something that obviously isn't broken?
As for the Top 100 list, Hernandez undoubtedly is the top pitching prospect in baseball. I think I'd take him over any hitter in the minors right now. But read on to see why he might not get the No. 1 spot . . .
If your curious about the last sentence I will fill you in. BA uses 130 AB's to decide who is a prospect and who isn't. Mauer has yet to reach 130 AB's, therefore it is likely for BA to rank him #1 next year. Though in MLB terms he won't be a rookie cause he has to much service time in the bigs.