Think of the recent NFL Draft, just days before the draft several mocks had Geno Smith going Top 10, a few had him Top 5. He didn't even end up being Top 30. In the MLB Draft, there are really only 3 guys you can be 100% certain won't drop to the Phillies: Mark Appel, Kris Bryant and Austin Meadows. The MLB Draft is virtually nothing like the NFL Draft. Even uber-prospects like Strasburg, Harper, Bauer, Bundy, Upton, etc. spend at least a season in the Minors, some, even great ones, spend several years in the Minors. Another difference is in the NFL Draft, the Rams didn't think Alec Ogletree was worth a pick in the late teens so they traded back to 30 and waited for him to drop to them. That's not an option in the MLB Draft (though, with the stricter slotting, it should be allowed now), if the Red Sox, picking 7th, love Phil Ervin, but normally he would drop into the 20's they can't trade back and take him there, they have to take him 7 if they want him. So, in the MLB Draft, all you need is one Org. to think a guy is the next cornerstone for their team and all mocks get thrown out the window. So, just keep that in mind with these previews, it could all be irrelevant in 3 weeks if teams like certain guys more than the community at large.
From here out, most of my previews will be of hitters. Not that there aren't good Pitchers aside from Shipley, but because the draft is somewhat shallow for hitting and if the Phillies want an impact bat in this Draft, it will have to be in the First Round. There should still be good Pitching prospects in the Supplemental and Second Rounds.
Justin Williams is a 17 year old High School Outfielder from Houma, Louisiana. He stands 6'3" 215 lbs (some reports say 6'2", but he's 17 and as I recall from that age, height changes often enough he could be 6'4 by Draft day, so I'll take the higher number) and has the most Power Potential of anyone in this draft class. He's a converted Shortstop, but he's likely not athletic enough to be a Center fielder in the Majors. He'll be much more likely to play a corner OF spot (has just enough arm and just enough speed for right. Instincts remain to be seen), it's possible he may even end up at First as he grows and slows (though he should have enough power to stick there). He's a Left handed hitting power bat and right handed thrower.
Now that we covered the basics, let's look at some video and what there is to like about him and dislike about him. The first thing to like is the Power as he won the HR derby at both the Perfect Game and Under Armour All Star games (no small feat). What I like in the video below is his bat speed, which is great and generates his prodigious power. At first glance I also liked his swing mechanics which include not even a foot lift as a timing mechanism, then I watched more and more and noticed he very subtly dances in the box before the pitch. That's a bit of a mess that will need correcting. Watch around the 1:00 mark of the Home Run Derby and you'll notice he rocks back, forward and back before each swing. He compounds this by also wiggling his bat before some, but not all swings. One nice thing he does is he doesn't swing his eye off the ball (at least in the clips I've seen).
So the swing will need work. Scouts seem to indicate he has a good feel for the strike zone, but struggles with off speed pitches. Ultimately, how many high school hitters don't struggle with off speed pitches? The video below isn't action packed, but it is somewhat exciting as you see a prodigious power hitter with the patience to take a walk, then, in the second AB, take a mighty hack to go down 0-1 and lay off several close looking pitches to draw, yes another walk.
Williams has very prodigious power (during his HR Derby he launched several shots into the upper deck of the Metrodome), a pretty mediocre arm, average-ish speed, a good eye and perhaps needs some work on pitch recognition and hitting mechanics. The off-speed issues don't bother me a ton as virtually every high scooler needs to do that work. The patience is awesome, but the mechanics are a potential big red flag. Some guys struggle to change mechanics they've used for years and suddenly power goes away or patience withers. This change is minor enough that I don't exapect it will completely derail the kid. A lot of scouting reports will note that his power often doesn't show up in games. I would venture this is largely due to the lengthy dancing in the box that in the second video you can see he is still in the middle off when some of those pitches pass him.
Two years ago the Phillies drafted a raw OF with a big body and prodigious power potential, so it seems logical they could go that route again. Williams seems to keep himself in better shape, perhaps than Greene. Plus, unlike Greene, there's an outside chance that maybe Williams could even play the Hot Corner. That would certainly be nice, but I doubt that happens. Overall, I like Williams a lot. I expect he can make the Majors as, at worst, a Fourth OF. At best he's a future All Star with the power to win a few HR crowns.
There are a ton more videos here at Perfect Game, where you can see some progression over a few years.