He is considered a bit of an overdraft, as he was ranked #236 by Baseball America in their Top 500 draft guide. That is more than 4 rounds ahead and is slotted for $144,300. That is a difference of $268,000, so one might assume that he will probably sign for under slot, and possibly by a significant amount.
He used to be a pitcher out of high school before converting to a hitter in college so his Perfect Game profile is actually from his days as a high school pitcher. They didn't feel the need to update it when he made the conversion to OF with Wake Forest, so that would help explain why BA ranked him so low.
Here is his bio from Wake Forest's website (it has a video of him there):
Walter [coach] on Williamson "Mac is a five tool player who is just coming into his own as a hitter. This past summer he made great strides and has turned himself into an elite prospect. He is the kind of player who can take over a game. As he goes, so will we."He hit .286/.396/.589/.985 (stats) with 17 homers and 42 runs with 52 RBIs. He was second in HR in the ACC in his redshirt sophomore season (started every game in LF) and was tied for league lead in homers this season with 17 (though led in homers per game by good amount 0.32 vs. 0.29, he was one of three boppers then the next tier). With his homers, he ended up 3rd in SLG, though just barely beating out two other guys. He was the best junior by far for homers; though remember, he's actually a senior by age, and was tied with another senior. Still, the only other junior in the top 10 had 10 HR in 10 more games (and Mac had 12 when same age as the juniors).
Not that great a batting average, .286 was right in the middle of the league. Though when looking at the leaders, #24-25 was only .295 out of the qualified hitters, so he was not that far off from the leaders when only taking qualified hitters into account. That is a difference of two bloop hits falling in instead of being caught, between him and being in the top 25.
And while he exhibited some speed with 12 SB (he was tied for 17th but one more would have put him in tie for 14th, and one more 12th) out of 15 (tied for 15th in league), that probably was more related to being smart about taking a base when the opportunity is right, because he only got 7 doubles, despite leading the league in homers (though tied). Good success rate of 80%.
He has a below league average BB/K ratio of 23/41 or 0.56, and almost league average contact rate of 79%. He also got 13 HPB, which was among the leaders (he was tied for 7th), though there were a lot of guys with 10 or more HBP, so that is partly the league too, it seems. And he was 25th in OBP, but could have jumped to 19th with a couple more on-bases. BABIP was .284, just to note. League BABIP was .325, contact rate was 80%, 0.64 BB/K ratio, FYI, so he has poor contact skills.
At least he improved year to year, for the most part, culminating in this past season. His contact rate was on an up trend: 70% in freshman, 72% in sophomore, 79% in junior (remember, all redshirt years), which was almost league average. So did his BB/K: 0.28, 0.43, 0.56. BABIP as well: .244, .222, .284.
Lastly, he was 13th in fielding percentage, for what that's worth.
His school's draft announcement noted a few interesting things. As noted above, Perfect Game only had his high school profile of him as a pitcher, and this PR noted that he came to Wake Forest as the "number one pitching prospect in North Carolina," and yet they switched him to a hitter sometime in his red-shirt year. It noted that he played all three outfield positions during this three years at Wake Forest, collecting 12 career outfield assists. He said that it was kind of a shock because he didn't get any calls that day beforehand (which is not a surprise, he was ranked much later, around the 7th or 8th round, by BA).
A news article noted that Mac had 36 home runs and 35 stolen bases (out of 47, 74% success rate) in his three seasons, and a "plus arm in right field."
Here is a blog post in early February discussing Mac:
rJR OF Mac Williamson, a favorite of scouts for years, has long tantalized those who have seen him play with his five (four if you don’t like his hit tool as much as I do) potentially average or better tools. His numbers as a redshirt sophomore (.293/.389/.532 – 27 BB/55 K – 205 AB) give some hope that the improvements shown in approach can help him demonstrate his above-average raw power more easily during game action. ...
I can’t wait to see if Wake Forest OF Mac Williamson (Round 46) can put it all together in his redshirt junior season. He’s a legit five-tool prospect who has made great strides in his approach to hitting since arriving at Wake Forest. From a pure tools standpoint, I’m not sure there are five better outfielders in all of college baseball. The biggest strike against him for me is the fact he’ll almost be 22 years old by the time next June’s draft rolls around. …
Williamson, a potential catching conversion candidate at the pro level, has serious power upside and a plus arm, but his swing at everything approach could prevent him from ever getting the chance to put his crazy raw tools to use. He could very well be viewed as a potential late inning relief prospect because of the reported mid-90s heat to go along with a solid sinker/slider mix.I've never heard of this site before, so I can't vouch for it, but what he wrote jives with what I've read about him and thus I wanted to bring this up since it does provide another view of him, though I don't know about the catching or pitching speculations.
On the face of it, he seemed like a good selection, in the third round, you expect to see a number of flaws in prospects, but most critiques of this pick is that he was a reach. And that makes sense given BA's mid-list ranking for him.
So I thought I would look into his sophomore year, when his age was a junior, to get a better comparison (though with one less year of college competition, he was behind other actual juniors). He was still fourth in homeruns in 2011, which is still pretty good and bunched up with a number of other guys. In fact, Shaffer had more HR with 13 (Mac had 12) but then fell to 10 in 2012 while Mac jumped to 17. So he has similar homerun power with the first rounder (25th pick; much better peripherals though than Mac). But his BA, OBP and SLG were much below the Top 10 leaders in 2011.
So he profiles like a lower BA hitter, average number of walks so his OBP will probably be below average, good defense and arm in the corner outfield, and enough speed and savvy to get in the high single digits in steals, with his main skill being power, and mainly homerun power, as he does not get a lot of doubles.
I have to think that while the Giants drafted him because they like his power and defense, part of the reason is because they think that they can sign him to a lower bonus than slot, which could free up funds to sign up picks who might want more bonus in the later rounds. The Giants are already above by roughly $75K with the Shilo McCall signing, but each team can go over by $400,000 and not be penalized, so any money saved on Mac could be used to sign another prospect, should they need to go over slot.